Advice for a newbie

Hi. Hoping to get some advice on my swim routine: I'm 47 yr old male, 5"11"+, 215Lbs (yeah that's right - 'bout 40 lbs overweight). I used to run competitively in HS and college. Ruptured a disc in my lower back many years ago ago and have spent many years and numerous procedures/Docs attempting to find a minimally-evasive fix. This is part of the reason I have put on so much weight. All efforts have been to little or no avail. Docs say that barring full-blown surgery, swimming is the only exercise they would recommend. So swimming it is (I've decided to not try surgery and live with the pain). I have been swimming off-and-on for about 3+ months. Most of what I have learned about swimming techniques and workouts have come from this site. And it has helped take off some of the weight (I was up at 230). But I am finding motivation and plateau-ing a problem now. Due to work related travel I also cannot work out consistently, sometimes not swimming for a whole week. So, in an effort to keep up my motivation and interest, I have decided to join a local masters swim team. I am more than a little worried that I will not be up to the task as I have never swum competitively before or even in a group for that matter. Sorry if I have overshared, but here's the question: Given that the team workouts will start in about 3-4 weeks, what modifications to my workout regeime below would you suggest to prepare me for the team workouts? Sunday - no workout Sat - 1,550 total scy - easy swim (31 minutes) Fri- 2,250 total scy - 200 warmup then 3 minutes rests inbetween the following sets: 4x50 :50 pace 4x100 1:50 pace 4x200 3:45 pace 4x100 1:50 pace 4x50 :50 pace 50 warmdown Thurs - 1,800 total scy 50 warm up 1x1600 at 29:15 150 warmdown Wed - 1,200 total scy 8x100 2:00 pace 1x400 at 7:40 Tue - no swim Mon - no swim All swimming has been in freestyle as my ***, back, and fly are pathetic on a good day. I was pretty toasted after the Friday workout . . . any suggestions on what I should do over the next three - four weeks in prep for the team workout would be appreciated.