Good luck finding any of the 20 series any more. They are all but extinct with the Stage III compliance rule in effect.
As for the 30 series, the 31 is very different than the 35. If you are going to be flying a specific model, get some sim time in that model.
The 45 carries over a lot of Lear similarities, but as stated before, it's a completely different and more expensive type rating than the LRJET.
I love the Lears! They are a lot of fun to fly. My favorite is the 31. Brake release to FL180 in 2.5 minutes!!!! Little rocket.