BPA

Yes, of course there are certain criteria which you need to fulfil before you apply for a transfer. And, also you need to first check with BHU officials, if they would consider you for admission in 2nd or 3rd year.

For admission in BPA course, you need to either have 10+2 or equivalent examination or a Graduate/Postgraduate Degree; and (b) Vocal Music (Hindustani, Dhrupad)/Instrumental Music (Sitar/Violin/Flute/Tabla)/Dance (Kathak/Bharatnatyam) as one of the subjects in any of the above courses and the candidate is passed in this subject also; or passed 3-Year Diploma in Vocal Music (Hindustani, Dhrupad).
For more details visit: https://www.shiksha.com/arts-fine-visual-performing/music/course/b-p-a-in-vocal-north-indian-classical-music-banaras-hindu-university-varanasi-271497

No, there is no uniform for the BPA music course.

You can prefer R.S Agrawal for aptitude in order to improve your aptitude section.

Yes, basics are taught at the starting of the course.