Don't think I performed well in CLAT at all. Unlikely to be even in the top 1000 ranks. Will this affect my future prospects?

You will be a non-NLU student and would have to work harder for securing internships because of the discrimination between NLUs and non-NLU students. Getting into tier-1 corporate just after graduation will be difficult.
Faculty depends on the college your select. Some will be bad, some will be good.
But all in all, it boils down to what you want to do. You can excel even even if you are not from those top-5 NLUs. But you must start early and have a clearly laid out plan

Don't choose law unless you're super passionate then. Or have contacts in litigation/law firms. Lots of better options. Do a good undergrad degree from a good college if you have the scores and then decide

I am passionate (cannot add the super because obviously) about law, and am sure abt getting into nlsiu or nalsar. But i have no contacts, nor anybody in my family in the field. Is the latter so necessary?

Not if you're in a good college, alumni networks and college cells do a lot for you then. But if its a less recognized college, then yes.

No it's not. Loads of first generation lawyers from those colleges have done really well.

AILET is still left. I know it's hard, but you can still try getting into NLUD. Don't lose hope yet. All the best.