Difficult to see from the picture, but if gluing your two halves together will leave a join line that will form part of your mould then feels like you need to glue then paint the whole pattern in one go.
Number of coats will depend on the finish you achieve on your first coat, but key between coats if you need to build up a decent thickness of coating to flat back. Spraying will give you a better finish but if the part's not overly large then working through the brush marks shouldn't be too bad. It's likely that you'll break through to the pattern surface at some points, so might be best to re-coat only when/if this happens.
A foam pad or roller might give you a better finish, though, if spraying's not an option