The advice here is good: if your maximum expense is one grand, then think semi-modular. Many different models to choose from, besides those mentioned. Assuming you are in the USA, your budget can get you one of these:
- Pittsburgh Modular Microvolt 3900 ($630)
- Pittsburgh Modular SV-1 Blackbox ($700)
- Kilpatrick Audio PHENOL ($700)
- Dreadbox Erebus III ($600)
- Dreadbox Nyx V2 ($600)
- Moog Mother-32 ($615)
- Make Noise 0-COAST ($540)
That leaves you money for a keyboard. Or just get an Arturia Minibrute 2 ($500). Later, you can expand any of these with another semimodular or a modular.
Don't forget some sort of fun effects. Standard recommendation is a Zoom MS-50G.
Or just get a Arturia Microfreak ($340) and bank the rest of your money. There's no reason to think a non-modular synth is too limiting. Internal routing is the same as modular patching! Both allow you to make new connections in interesting ways. The differentiator is the flexibility. The Microfreak essentially has the engine out of a digital VCO, plus so much more.
I spent years with only a monosynth and a crap drum machine. Had loads of fun!