As for the percentage of FTP for the 2x20s: go by feel and do not go out too hard. The important thing for a new PM user isn't to be so uber precise with the numbers, but to get in the time near your FTP. The more you do, the more you will get a feel for what your body is capable of doing. Don't be afraid to start out your 2x20s at, say, 230-240W. If the first 20 min feels too easy then try to go 5W higher. Try to go easy at first. 240W will feel slow, but use the PM to hold yourself back. If you go out at 270W you will feel like a rockstar the first 5 minutes and the last 5 will kill you.
On Tuesday, maybe go by how you feel and just ride. Or go jump into the crit; there's nothing like getting spanked to spank you into shape.
Take Wed off, and recover! *recovery will help you loads*
Thursday try a 2x20, maybe get in 2 hours but the other time can just be spinning around.
If you are having issues with volume and intensity then I think you need to work into a super hard day after Thursday. SST my friend. http://www.fascatcoaching.com/sweetspottraining.html
Saturday needs to be about the miles, do big rides. Even if they are not fast get in the big miles. Be sensible and progress, 50 miles this weekend, 60 the next, and so on. It won't take long before you can go out and do a big ride that is fast.
Anyways, I said a lot and could probably be corrected on some things. I'm not a coach, I've been riding for 2 years and using a PT for 3 months. What I say is not the authority, but I hope it helps.
Oh yeah, and this is something I (need to and do) hear sometimes. "Chill out about the numbers and geek stuff and just ride your bike" I sense that maybe you are like me and get a little obsessed about power, and training. So numbers are great, but they aren't everything, so just ride your bike and have fun!