nothing special Lists one of the most demanding games of the decade
In all seriousness, without a budget it's very hard to help you, but here are some pointers:
Nvidia 3xxx series cards are huge because of the heatsink, but the PCB is actually fairly small, especially on founders edition cards (sold by Nvidia). If you can figure out a way to cool them they make for pretty powerful small cards.
However, Nvidia gatekeeps VRAM in their cars so you buy their $10k special boy ai cards that are just cards with a shitton of vram on them. AMD is coming around but I don't think we'll see much improvement until next gen.
CPUs have flipped again and now AMD is king for gaming. They are also kind of nice on the heat output, making them a prime choice for sffpc.
Everything else you listed is just a factor of RAM. Go with 64 Gb since you're going to load large models, and that'll cover you for a while.
We are currently on the cusp of the migration to DDR5, but we are just about at the point where the best DDR5 sticks outperform average ddr4 sticks. Either wait about a year or go with ddr4 ( which severely limits your upgrade options)
If you've been out of the PC game you may not be aware that SSDs have become tiny, through NVMe drives. They are a tad more expensive but since you want small that's what you want.
They also make small form factor power supplies now, which was a problem for a while. If you want really tiny, they even make laptop-style PSUs that end in a 24-pin connector instead of a barrel jack, but you're not powering a dedicated GPU with that.
PCIe extenders ("raisers") are commonplace now, that might help you to fit a GPU in a small case.
I'd suggest looking around on PCPartPicker which is still the definitive source for compatibility options and pre-selected builds that actually work well.
And finally I'll add a word of warning: small form factor is hard as fuck. If you haven't built a PC in a while (I'm assuming you still know how to, it hasn't changed that much) I'd suggest simply going for a regular ATX build before embarking on the nightmare that it is. Also, small form factor cases are generally a compatibility nightmare. In general, you want to pick a case first and then pick components that will fit in it.