I agree with most of the things you said, although I suppose I can add a bit for the people who are wondering for something more in depth.
As Bringer said before Yoshi is a mainly defensive and counter based character, so stages for him don't really matter as much to him as it does for someone like a SA. If it's not already obvious, you should just counterpick with stages that you feel the most comfortable with, since there aren't any stages that completely **** Yoshi, and nor are there any thatcompletely benefit him either. Yea, try to go along with the opponents weaknesses too, don't be an idiot and go around countering peach and Jiggz with MC.
Also I think that the stage counterpicked is based on your style. Personally I enjoy counterpicking with stages that give plenty of room, as I'm a very aggressive, fast paced, and combo-oriented style of Yoshi, although my other friend who is an extremely campy and defensive Yoshi prefers platforms for his slower egg-based combos and set-ups. Both of them work to benefit our styles of play so that's just how it goes down.
@ Bringer - I'll agree that Yoshi doesn't have the best platform tech game, but I think it's much better than the options he has in regular tech-chasing. More options are open to you since they have no decent movement (after teching on a platform) and this makes them much more easier to punish, as opposed to them going way too far away to pursue with anything other than an egg, by teching in a large area. Just my opinion, but then again that's prolly just me sucking at techchasing. xD
Also the comboing is good on any stage, if you know how to use the platforms correctly, platforms are good juggling friends, and I <3 them very much, plus eggs are much more annoying on platforms.