Lots of good questions.....unfortuanetly if you want a stable set-up that will support corals, your budget may have to increase.
Anyway to your questions.
For a CLS on a 55gal, depending on wether or not you use a spray bar, you are going to want at least 1200-1800gph flow.
For your sump return what you want to do is match your return pump flow to the output of your skimmer. (You will want a good skimmer) I would buy one that is rated about 2x higher than your actuall water volume.
For softies and LPS T5's will be suffiecient. If you want clams you will need at more bulbs, and individual reflectors.
You may want to do some research on substrate. this will help you make a ton of other decisions on lighting/flow/ and amount of LR.
For filrtation all you really need is LR and as stated above a good skimmer..
Hope that helps a bit, I am sure lots of other people will have a TON of other suggestions and comments aswell.
Goodluck and welcome to TRT!
