how many minimum courses to complete on F1 visa to avail OPT of 29 months


Please advise on following:

I have applied Change of Status (COS) from H4 to F1. Currently I am doing M.S. in IT from a US university. I will get my F1 probably around December end and I would have finished 4 courses on H4 by then and only 8 courses will be remaining for doing on F1 visa.

I want to know how many minimum courses do I need to complete on F1 visa, to avail OPT of 29 months. 8 courses will be devided in 3 semesters (4+3+1 = 8).

Should I wait for my F1 visa or I can finish 4 courses and do rest 8 courses on F1 is sufficient to meet USCIS requirement for F1 visa OPT.