firstly I would go for a bigger case - it may save you buying a second case and therefore money in the mid-long term... the best bang for buck starter cases are either tiptop mantis or doepfer lc9 - if you are intending on more digital modules then I would recommend the mantis more (and it is more portable, if that's an issue) - however both are probably the best combinations of hp/cost/good power supplies from respectable manufacturers available
otherwise it's kind of an ok start, depending on what instruments you are thinking of processing...
if all you really want is some filtering and granular processing - I would seriously consider (ie spend a month or 2 thinking about it) whether you really want to go modular or whether a few effects pedals will suit you better - they will almost definitely be a less expensive solution
your starting idea of an input module with envelope follower and a sound processor is good (but see below)
if your sound sources are stereo then a second ears or similar module (pre-amp with envelope follower built in) is a good idea - mostly so that you can extract the envelope shape of both the L & R channels for use in modulation, rather than just one
if your sound source is mono, for example a guitar, then I would strongly advise the addition of an expression pedal interface (examples are available from ADDAC, Doepfer and 7 dials) to enable you to play the guitar (for example) and still control your effects - in fact you may want more of these - otherwise you would probably be better off with more effects pedals - a wah pedal instead of the filter and I'm sure there are granular synthesizers in pedal form these days
as for your module choice:
ears - owners seem to like it so it appears to be a good choice although I've never used one - I have a doepfer a-119 instrument interface module - which adds a comparator (a gate opens when the input signal excedes a set voltage) and adds grit, shall we say - and is slightly cheaper - there is also a chip swap (no soldering required) that can be done to reduce the grit but I have never felt the need - furthermore the gate output can be extremely useful as a replacement for or alongside a master clock - nb a lot of modules need steady clocks to operate properly - Pams doesn't work well for example, nor any modules that multiply clocks - dividers and modules that provide triggered lfos or envelopes tend to work much better
maths - great module - although I always recommend both downloading the 'maths illustrated supplement' and working your way through it AND replicating it's basic functionality in dedicated modules - maths is much greater than the sum of it's parts - and you will need those parts separately as well to allow you to use maths to it's full potential (which points us back to the illustrated supplement)
humpback - this is a DIY module - I don't know if you can buy built ones, I've never seen them - are you skilled and do you have the tools to build it? if not I would consider an already built filter - doepfer make a great selection of reasonably priced ones - based mainly on classic designs - or there are many more available at differing price points - if however, you intend to buy a soldering iron and build this - I would also suggest building some simpler modules to start with - a passive mult, an attenuator (thonk atatat) and some of the AI Synthesis range would make the learning curve easier and less frustrating for you - again you may find you want 2 filters or a stereo filter instead of this
clouds - are you intending on trying to find one used? or a clone? it has been discontinued for a few years and has been replaced in the mutable line up with beads - I would spend some time considering this - read reviews/watch youtube videos of beads etc - mutable support is fantastic, but understandably stops at 3rd party clones - most of which push it into poor ergonomics territory (eurrorack is already very small without miniaturization of modules) - supercell is a larger cloen with a few extra additions and may be worth a look
the vca - ok but personally I would replace it with a veils - it will initially work as a mixer too, but I think that you'll want more mixing - and particularly something that can handle stereo output (see erde-verbe section below)
erde verbe - great reverb for emulating 'weird spaces', but not a particularly good general purpose reverb - takes a mono signal and outputs a stereo signal - you may really want a stereo to stereo (to add more reverb to clouds) or a mono reverb (depending on the requirements of your output - stereo/mono)
Pams - hmm - not really a function generator as you described it - it's more of a master clock, clock divider/multiplier with some synced envelope generation/lfos - whereas function generators generally apply mathematical functions, such as slew to incoming signals and extract events from these signals - so in some ways similar to a function generator, but not really - note it's heavily synced to it's clock (internal or external) which may not suit you depending on how you intend to use the rack and how accurate your timing is with your instrument - I'm human and so a bit sloppy at the best of times - which can be both a good thing and a bad thing, depending on your point of view and what you are trying to do!
further effects processing modules - more filters - and I would look seriously at the happy nerding fx aid xl - very versatile - I would make this an early purchase as it can be used as a filter - as well as reverb, delay, lofi etc - if I was designing an effects processing rack I'd probably include 3 of these due to their versatility
utilities - you'll almost definitely want more utilities - seemingly dull inexpensive modules that appear to do nothing to alter the sound (they are the dull inexpensive polish that makes the expensive shiny modules actually shine) - they are incredibly useful for not only improving the patching possibilities - but also for solving problems - like (auto-) panning a mono signal into a stereo space, or switching between multiple inputs into a single output or vice versa, or reducing the amount of modulation that is sent to an input (especially useful with clouds - it's modulation inputs really need attenuators! I usually recommend a great utilitiy starter set of mutable links, kinks, shades and veils - or modules that cover their various functionalities - wmd/ssf toolbox and happy nerding 3*mia make good substitutes for some of these funcionalities
mixing - seriously consider how you will mix mono & stereo audio signals together and which modules have mono/stereo inputs and mono/stereo outputs - and the possibility of parallel processing - you will almost definitely need multiple mixers - some for sub mixing, one for end of chain mixing and some for mixing modulation sources - some of which should be voltage controlled - and this is on top of what you already have in the rack - I'd definitely recommend a matrix mixer - both for mixing modulation sources and for
moogerfooger - luckily these are some pedals that really don't need an effects pedal interface to reduce the signal down to guitar level and bring it back up to modular level and correct any impedance issues - I have 3 of them and have used them quite a lot with my modular - a lot of other pedals really need the interface to work properly
"some of the best base-level info to remember can be found in Jim's sigfile" @Lugia
Utility modules are the dull polish that makes the shiny modules actually shine!!!
sound sources < sound modifiers < modulation sources < utilities