You have everything you need to get you started, really.
40 gallon tank - get a glass tank; cheaper and doesn't scratch.
3x powerheads - maxijet 900's
- 50 lbs...get smallish to medium sized pieces
Sand - Get enough for about a 1 inch bottom...good luck finding cheap sand
refractometer - order one from liveaquaria.com. Best $40 you will spend
test kit - to include ammonia, nitrate, nitrite, ph
Salt - I use Instant Ocean
shrimp from the supermarket - 1 for starting the cycle (the LR
may also be used to cycle if it is uncured)
protein skimmer - aqua remora c pro...don't go cheap, get the Pro
Lighting - Ahhh...the big question. You still have not really answered what you will keep. I would just start with a normal strip light at this point.
That will get you started. It will take 1 to 2 months to cycle. In that time you should have your stocking choices picked out and have decided if you want to go reef or not.