My suggestion is don't put him on the bus. Period. Especially since you are a SAHM, just drive him. I know you have a little, little one at home still, but I'm sure his schedule could be adjusted if necessary. My eldest is 13 now, but when he went to Kindergarten, he was just a month into his 5th year...he was so little!!! I was a single mom at the time and I just cried and cried...and then I had to re-do my make-up and go to work! It stunk! He threw up on his first day and I couldn't even be there for him for right away, because it took about 45 minutes to get home from work! I would have given just about anything to be able to stay at home with him and drive him to school.
The concern I have with the school bus (and school in general) is the things that go on during "non-scheduled" school time, like bus, lunch, recess. In our district, each grade school has K-6. That means the little 5 year olds are riding with 6th graders! I think that is simply ludicrous! That is actually one of the reasons I am planning on home-schooling my other kids (4 and 2). I just don't want them receiving the "education" from the older kids. I have a very high regard for the public school system, and my eldest is still in it and will continue there, but it's just what we feel is best in our situation.
But enough of my story...I think simply committing to driving him would be a lot less traumatic than following the bus, and besides, what would that accomplish other than seeing that he got there safe. If you drive him, you also have your "special" time with him to encourage him for the day and also find out how his day went...think about it...he certainly has a captive audience! Plus if something traumatic happened or something wonderful, you are already in the car, so you can just turn it towards McDonalds and make everything all better (or celebrate!).
Well, I seem to have written a book here...sorry about that! Oh and just to let you know...it really doesn't get too much easier. That 13 year old I have...I about cried last year when he began middle school and had to walk 8 blocks (talk about scared!!!) and I'm already tearing up thinking that next year I'll have a high-schooler!
I hope this helped some and I am sure it will all work out in the end...