2) What's a good system to show an invitational hand in nt
A modification to 4 suit transfers similar to what Taiga mentioned.
2S = bal invite or invite with long minor
2N = transfer to clubs, weak or slammish
3C = transfer to diamonds, weak or slammish
If opener shows a minimum over 2S (by bidding 2N), responder corrects to the safer minor suit partial with the long minor invite hand (which gives opener another chance with a fit).
There is no "pre-accept" on the minor suit transfers (since the invite option is now excluded).
The invite via Stayman garbage is eliminated.
You lose whatever a 3C response to 1N meant in your ver of 4 suit transfers.
Otherwise, other auctions are as in 4 suit transfers.