I'll start you off and others will chime in.
Your tent is about 3 1/2 feet by 3 1/2 feet by 6 1/2 feet for conversion purposes. A 600w bulb will give you about a 4'x4' footprint. 1.3m x 1.3m so 2 plants should be fine. An air cooled reflector would be nice.
As far as HPS many people use HPS all the way through....many use a T-5 or MH for vegging, then HPS for flowering.....different light spectrum. You can always add veg CFL side lighting if you want.
My first question should have been what's your budget? Throughout your grow temp and humidity will need to be watched...24C all the time is fine, but your HPS will heat the tent up and dry out the air. What is your plan for venting and odor control? There is also a good thread on "grow room design...we're here to help." Good info there.
What seeds did you buy? If you grow two strains you may want to keep their growing times close. Ask a lot of questions and if anyone flames...ignore them and do not respond.