Yes, I tend to sell / buy one or two players a season, and I'm probably more likely to keep draft picks than other teams. Last season, getting relegated from the English first division meant I got good draft picks, so two of them are in the side and training well.
And, yes, particularly for defensive skills - if I'm buying a new inside player, I insist on them having at least reasonable OD since I know I won't be able to train that. Likewise, I expect guards that I buy to come pre-packaged with OD and RB. I do still train those skills for the players who need them, but they take second place to 1v1, outside shooting, passing, etc., which can be whole-team trained.
You're right about expense and experience. I noticed in the the first couple of seasons, that my team finished games badly. I knew it wasn't stamina or game shape, and I think experience was to blame.
Overall, this approach probably made my first few seasons harder than it would have been for a 'traditional' train 1 or 2 positions and fill the other half of the court with experience team. But (a) it's only a game and I enjoy knowing that my players have been with me for most / all of their career, and (b) it's a long haul, not a sprint, the result of this approach is only now starting to show, and I think success will be all the sweeter for having been home-grown.