does change from BPS to IT in tcs affect compensation ?

It benefit you for appraisals [if happens] and technical learning courses

Also BPO3 are eligible for Wings2 but equivalent C1 grade is not eligible for wings2. So if you are in that grade and have already started your journey, then first complete it in bps allocation only

No. They will give same package. Also the free bus pass and other facilities will be chargeable.

Very minor

I accepted my department change request yesterday. From bpo3 to c1. Pay scale will be the same. And l don't have the break up yet. If there are any changes, i shall update