with your budget would probably suggest a 1000 hps lamp for flowering and a 400 mh for vegging both with air cooled reflectors.
suggest you have the flowering area about 4 by 4 ft wich would give you a little over 60 watts per sq ft, you may not want to make any walls to permanent as you may want to expand the flowering room at a later time.
you do want a seperate area for veg growth and to keep any mother plants you may have so you can take clones as needed to be ready to go into the flowering room.
a cloning area wich are often started under flourecent lights in a propagation tray and can even be set on a set of shelves until roots develop then moved under the hid.
as per number of plants to start from seed probably about 6 of just one strain at first let them get mature discard males and take clones off the females and flower the clones in the flowering room in a sog style grow at about 1 plant per sq ft or 16 in a 4 by 4 ft area.
you can always add other strains and discard any mother plants you do not want to grow out again.