Errr...sour...You said it all. You left flying Fw190A8, and that is what loses you.
answer to 1):I never go faster than 510 IAS in a dive. The compressibility happens at 540-550 IAS (at 10K or so), so there is no way I can compress the 190.
Answer to 2): REverse like in a Fw190A8. Fly A5 like a 190A8. The most common error in MA is to see fw190A5s turnfighting. Sure, they can turn very well at hispeeds. The problem is that they wont be at hispeed if they turn too much.
So BnZ. Best way to reverse?->always in any plane keeping E up?, low G immelmann. There is no secret it it, the problem is that depending the situation, a high yoyo can be more adequate,or a hammerhead, or a tight immelmann or a...you get my point.
I tell you seriously, if you want to master the A5, master A8 first. Fly both equal, and you'll find that A5 keeps E much better, and close fights very well too. Use the first to E-fight. use the latter to defensive moves. But dont try to close fight on the offensive because you wont be able to keep it for long.