I hope I can help because I just finished another one of these this weekend. First you do the seed stitch back and forth on the sleeve stitches. Once you have the sleeves worked and bound off, you will have two little sleeve flaps and your back stitches on a holder. Put the bottoms of the sleeve together, matching the seed stitch bands in the round and seam about 1.5 inches only (up to raglan "seams").
I know it will make sense when you get there! Go ahead and do the seed stitch and the place you need to seam will be there.
I made this sweater a while back and I had the same problem. If I recall, the pattern does not go by any number of rows, you mostly knit in stockinette for a certain number of inches. So the row guage is not really a problem.
When you join the body pieces, you skip the sleeve stitches and cinch the body and the back together. The first time, the stitch is a little awkward, but there is not a huge gap where the sleeve stitches used to be. You just push the sleeves out of the way and the body continues without them. I know you will do great once you are actually there! The straight needles must make it really confusing because you can't hold it up and see that it actually kind of looks like a sweater.
I have a bigfoot boyfriend, too! I just made him a pair of socks and I was worried that after I spent all the time on them that they wouldn't fit. The lucky thing about socks is you can just make them as long as you want, and I covered my bets by making them in a cotton/elastic yarn from Elann so they were stretchy. They fit very well.
So I would recommend making them in the Sock it to me Collection Esprit yarn from Elann.com