Welcome to IS bud. Ideally, you want to get your bf% a little bit lower before you start which could easily be done in a short time to prepare for your first cycle. Below 15% is recommended, the lower, the better. I wouldn't recommend pushing your cycle out to 15 weeks, keep it at 12 weeks your first time around. You're right considering test only as your first cycle. One compound is all you should run for your first time and your results will be awesome given that your nutrition and training is solid. Stick to the long esters, Cyp or Enan. Keep the dose low at 250 - 300 mg EW, your receptors are fresh so you should respond extremely well. Don't forget your AI. You want Aromasin for this, you can start at 12.5 mg EOD. You have to wait for the ester to clear before starting PCT. Here is an example layout that would work well for your first time:
Weeks 1-12 test cyp 250 mg week
Weeks 1-14 aromasin 12.5 mg eod
Weeks 11-14 hcg 1000 ius week
PCT Weeks 15-18
Clomid 50/50/25/25
Nolva 40/20/20/20
Aromasin 12.5 mg eod
MK-2866 25 mg ED
GW-501516 20 mg ED
Added some Sarms in your PCT. MK & GW, this is a crucial period where you want to keep your gains and these Sarms work to make that happen. If you have any questions bud, let me know, I'm here to help.