Hey, bR,,
I'm in roughly the same position as you - countless hours learning but some grow experience now.
My first grow was with a 125w cfl - not much use and wouldnt recommend it as I live in a fairly cold climate and like the lamps for their heat! I got nothing from this grow as I hadda cut the grow short due to house move etc so my experience is limited.
My present grow (almost 2 years later) was started from one seed I found in a bag and it has been vegged on a windowsill during summer months. This has resulted in a plant approx 1 m in height (solid Sativa strain of unknown genetics), now I've put it under a 400w metal halide for flowering. I know it probably should be HPS but that was the bulb I got with the lamp, may change it up yet.
My advice is to go 400w if you want to see some decent bud. It's my first experience with them and I think they run pretty cool (I do have a cool tube but no fans hooked up as yet) but hot enough to take the chill from the air where I live (coming into winter), running approx 10 inches from the small flowers.
Depending on strain, smell, grow area, local laws etc this will determine if you need ventilation. If you enclose the 400w unit then you should ventilate, if it is pretty open room then not an absolute.
Hope this a bit of help and if anyone else has any comments feel freel to chip in.
Togo