I'm unsure if my car has ever been flashed, so it might be locked, but how can i tell?
If you can't read, it is likely not stock.
Is it true i can flash with a stock ecu/map file even though i cant read the ecu?
Not if the ECU has a riser card where the flash is
If i can write to the ECU, can i or should i go to a higher revision?
In general, no.
There are other reasons to use a different revision though, not worth going into until you are ready.