Dan,
Some, short/sort of, answers to your questions:
1) Maybe - it certainly wore Luftwaffe markings before the Croatian ones - photos of the upper wings show overpainted Balkenkreuz and it's camouflage matches that of other MTT Regensberg Bf 109G-14/ASs in the 78X XXX wnr block - see Marc's excellent Flickr repo for more:
https://www.flickr.com/photos/280920...57625414158747
2) It's not RLM76, it's darker - it could just have been any grey they had available. The previously yellow(?) band in front of the empennage looks a good match for RLM74 seen elsewhere on the airframe.
3) Not sure what you're saying/asking here, but (under all the overpainting and yellow theatre markings) the airframe is in a (consistent for this batch of 109s) scheme of RLM74/75/76 with RLM 75/83 fin, again see Marc's flickr for more examples.
Hope this helps,
Chris