piggyback is not conversion, it is a certificate dependent on your foreign licence. (EASA PPL not UK CAA PPL I think you meant?) To get this one out of the way - You will need TSA for the CPL if you don't have a stand alone certificate, or you will need TSA for the stand alone certificate training so there is no difference there. You will need to get a 'piggyback' - 61.75 certificate anyway so you can log hours as PIC. That can use your EASA medical, which is validated as part of the licence issue process, but much easier/more sensible to get an FAA class 1 initial then use it as a class 3. The rules then simply allow you to do (an unrealistic minimum of) 3 hours training and if you meet all the other requirements for the check-ride entry (written test, hours,night hours,dual x-c etc) , to go for the private checkride should you wish, or continue through to cpl training. And yes, pic hours will count for Ir/CPL hours minima. First step in all this - become intimately familiar with 14CFR part 61 - it will answer most of your other questions about certificates/regulations . Start with 61.101 to 61.133
https://www.ecfr.gov/cgi-bin/retriev...n=14y2.0.1.1.2