No problem! It's nice to be able to contribute something here, since I'm new to the longboarding side of the fence and have been taking a lot of advice. I hope it helps you like your friend!
I'm on my second set of the lightknights - had a set of core Spitfires... flatspotted them, went back to the lightknights. I don't know how they make them flatspot-proof... just awesome.
Not sure what size ranges they come in - I ride 52mm on my shortboard. Perfect for shortboarding, hard as rocks for a longboard though, of course.
Just stretching by crouching like that, knees in chest, torso as upright as possible - maybe watching TV - if you can hold it for 30 to 45 seconds and then stand back upright...
I think the sign of progress is when you can lower yourself down into that position and raise back up again quickly and easily. Stretching is something I've been doing since my 20's before I go out to skate... if I don't, I pull muscles left and right if I really get aggressive in the slightest.
Definitely helps with flexibility too, though.
Good luck!