For NIT, being from ST Category, you must target atleast a ST Rank of 3000 for somewhat a good number of prospects among NITs. You may secure a Lower Rank till 3500, but then, your prospects decrease.

For a ST Rank 2500-3500, you must target a CRL anywhere around 150k in JEE Main or 85-87 Percentile. For 85-87 Percentile the corresponding Score will be anyhwhere around 70/300, which must be your Target. I would suggest you perhaps to target much higher, around 90-100/300, for excellent prospects during JoSAA Counselling, being from SC Category.