Well done so far. You ask about flatting it now, Normally I wouldn't do a full flatting at this stage, just remove any nibs or dust particles. However, You are planning on adding extra colours and it looks like you have a fair bit of orange peel in the photos. I would definately flat it off now starting with 800 wet & dry and finishing off with 1500 or even 2000, you have 5 coats on there so there should be no danger of going through but be very carefull on the edges. You will end up with a dull finish but you will get the gloss back on the final polish
Re the orange peel, you might need to add a little more thinner or possibly turn the pressure down a little.