to awnser your questions #1. what type of corals you plan on keeping? if it were me id go after a 175w mh pendent you can look for one here through sponser or possibly a used set up from a hobbiest here

200$ shouldnt be a problem to get a good light set up
#2 yes get a skimmer.... either a hob or one for sump use..
#3 refugium great place for nutrient export as well as a breeding ground for pods and good bacterias

is this a nessesity no.... but it will add more over all water volume as well as a place to hide all the heaters and what not

hth