I have a Feb bub and you really don't need a lot of clothes for them. Unless you have aircon that is run all day/night etc, then you wont need more than a singlet and wrap, with a jumpsuit at night. If you do run the aircon all the time, then you will probably just need some cotton onesies etc and it will be more than enough for bubs. The general rule of thumb is however many layers you have on, put an extra one on them, but of course if he is sweating madly then you would strip him down, likewise put a suit on if he feels cold.

ETA - as for hats, many of the tiny baby ones just don't cover their little faces well enough as the brims aren't wide enough. It would probably be best to get a shade cover for the pram and keep him out of the sun as much as possible.