Welcome to AquariumAdvice
with what you have from your old tank:
You likely wont need the canister filters. all the sand and LR
will be your filtration. Tank ornaments as well, you'll likely not like how they look in your reef. Keep the heater, if it was for a 55 gallon to begin with then it should be strong enough. The undergravel filter (assuming thats what you were refering to) you wont use. The rest is good, you will likely replace the two lights that are there. If you want to "go all the way" since you already have DIY
hood, if it has room, look into a MH
kit to install. at a minimum you'll want to put some PC
lights in there. THe ones you have now, (NO flourecents) will not be enough for a reef tank.
you're right on with what you need with the following additions:
for powerheads, you're going to want a total of about 600 GPH
between them and anything else that moves water in your tank.
For your old aquarium, have you ever used any copper based medications in the tank? if so, this can cause problems with many reef inverts. I'll let a few others chime in with if the tank is still usable that way or not.
Your plan for set up is good. after the sand water and salt are in the tank, add your heater and powerheads and get the tank "moving" once its up to temp, check your sg
again and adjust. if you're going to add LR
then putting that rock in your tank will start your cycle. If it is exceptionaly clean LR
(from a good LFS
for example) you may need to add a fresh raw shrimp from the grocery store to boost the ammonia to get the cycle going. Read up in our articles section
on Cycling, Curing LR
and there's a wealth of other info there too that I'm sure you'll find useful.