A couple of things come to mind for your situation.
First about your lack of a peg: Your clarinet did have one, but obviously it was separated from your clarinet at some point prior to you buying it. You should ask you tech if he/she has one in a old donor parts horn case that you could buy. It might not be a Selmer peg, but it doesn't need to be. All it is, is a piece of metal with a rubber foot that fits through the opening, and is held in place by the thumb screw at the bell.
I don't have a Selmer bass, so I don't know what the opening for that peg is, but with school instrument repair season being in full swing, there should be lots of horn pegs in the shops for techs to try out on your bass. Even if they don't have one in one their back room that fits your horn, if you could figure out which student model brand peg (if any) fits your Selmer, then if necessary you could always order a new brand X peg, and that would likely be much cheaper than getting a new Selmer one.
Why is it important you ask? Depending on what the angle of the neck is--and your horn is decades newer than mind, so it likely is somewhat better to start with--most bass clarinet teachers will tell you that a strap used in combination with the peg will help you get the mouthpiece at the optimum angle.
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Secondly, about your mouthpiece question: I know everyone says that Vandoren is the go-to bass clarinet piece. But you know what? I saved myself a lot of money by trying my tech's. It didn't work for me.
When I bought my bass clarinet from my tech just over a year ago--after not playing bass since university--it came with 2 mouthpieces: a Selmer HS* and the original no-name brand. I tried the Selmer, the no-name brand, and my tech's Vandoren--thinking I was going to order my own Vandoren. After trying his however, I found it didn't work for me nearly as well as both the MP's that came with the clarinet.
Then about 3 months ago I was looking through some boxes my tech keeps vintage mouthpieces in at his shop, and I happened across a Geo Bundy bass clarinet piece. I brought it home, and it is great on the Richard Keilwerth bass clarinet of mine. It plays beautifully even across the entire range of the horn, and intonation is simply a dream as well. Who would have thunk it?
The moral of this story is simply this: You have to try out a mouthpiece before you can determine whether it works for you or not. Based on what bass clarinet players all say, the Vandoren ought to have worked for me. It didn't. Now it could have been me; it could have been my circa late 1950s Richard Keilwerth-made bass clarinet; or it could have been a combo of the two. Whatever the case, mouthpieces whether for clarinet, saxophone, trumpet, or tuba, are a very personal decision. Play-testing before buying is always ideal. If that's not an option, then making sure the shop has a really good return policy is key to not being out your hard-earned $$.
One last thing about mouthpieces: Given that you're just starting out, have you found a teacher yet? It strikes me that finding a teacher would be a helpful step. He/she would be able to help you in eventually picking out a mouthpiece. At this point I'm not convinced you need one. Get the basics of embouchure; tone; breathing; breath control; etc, etc under your belt, then you'll be in a much better position to determine what kind of mouthpiece will work for you best.