I agree with Jynx - I'd stick the the 1.5 size. The 2's are smaller, and smaller = faster/twitchier, which is not the best for learning. Plus, if he's going to fly team or in any groups, almost all the group flying is on 1.5 size sails. . . . it's OK to get an SLE kite, as long as you steer clear of the SLE leading edge. It's big, heavy, and (relatively) indestructible, but the thinner spars (i.e. 3 wraps or similar) are far more common and fly better (according to most experienced pilots). Plus it's pretty unlikely that you'll bust a spar even if it's lighter weight (i.e. 3wraps being the most common thinner spar). That said, if you end up with a good deal on an SLE with the heavier leading edge, you can always reframe it in something else.
Don't forget . . . you'll need lines & handles as well. I know a guy from Kankakee who makes a mean set of snagless handles . . . and don't forget, Big Mike on this forum also sells Revs and line sets, if you are considering new. If you are set on used (and BTW, the majority of my collection is used, so I clearly think it's a good way to go), then the forums (and/or certain club members who have too many kites
PM me) are the way to go as long as you have patience . . . . or you can call a club fly some weekend and borrow our kites

. . . . I'm only about 1/2 hour from you.
KiteVoice - the SLE leading edge is quite stiff and heavy, which (IMHO) makes learning more difficult for a couple reasons. One, the kite is heavier so it's harder to launch & keep in the air in lighter / inconsistent winds (welcome to the midwest). Second, the stiffness of the spar makes it more responsive to inputs, which may actually be detrimental to beginners. Beginners have a tendency to overdo the handle inputs, which the SLE leading edge more fully transmits to the kite. The thinner leading edges flex a bit, and this means (for better and worse, depending on the situation), there's a bit of forgiveness in the LE. On the plus side, you could drive nails with the SLE leading edge or use it for tomato stakes, so you can bang it into the ground without worrying. To add to the confusion, older versions of the "SLE 1.5" were available or could be reframed with the lighter frame so an "SLE" kite might be a 1.5 without the SLE leading edge. An EXP is the same size and shape as the 1.5 or 1.5 SLE or the 1.5 B-series, and the spars are interchangeable. Think of it as the VW vs. Audi. Same manufacturer . . . some shared, some different components, and different engine tuning. Both get you where you want to go. It has a different panel layout, different fabric (not as "stiff"), a less expensive bridle, and "no label" spars (that are essentially 3 wrap spars). Personally, even though the EXP is less expensive, I enjoy flying mine, and I fly it more often these days when I need a full sail than my original (well used) 1.5 SLE (which I reframed in 3 wrap LE).