lyfsux a Skimmer is a very important piece of equipment. You have to look at the system as a whole and how you are going to deal with detritus and waste. Being that it is a pred tank with no corals it means that levels of nitrate are more acceptable as the fish can handle them. The two main fish you have are very messy and eat quite a bit. So your main focus is going to be on dealing with their waste. The ray like to bury itself in the sand, it also likes to jump on top of prey on the sand, so you need sand or cc and with him going in their your going to need to clean it, thus the syphoning. With a pred tank WC's are a big thing also to deal with the larger amount of waste. So with water changes, syphoning and a wet/dry style sump you should have things covered. Now you can get a skimmer I just think it wont have the impact because your going to have to do the above. You would be better off in this case to get a decent UV and use Ozone. That make sense or am I explaining it wrong??
Plus my Basement is unfinished so I am going to finish it around the tank a sump idea seems to be a better filtration system do you agree?
A sump doesn't do any filtration, it just adds water volume and gives you a place to put equipment. So for that no problem but I would still go with a wet/dry concept in the sump. this would convert your ammonia to nitrate which the fish can deal with and then your syphoning and wc's will keep those levels down.
On the LR, most folks use it as a filtration source, In a FO pred tank it will have no chance to keep up with the bioload you will be throwing at it, So I would say put in as much as you want but do it for decorative purposes and not for filtration.
Heres the concept. FO pred tanks are high waste producers, So biological filtration will be way overwhelmed and should not be relied on in this case. So not a big emphasis on LR or LS. Also because the preds eat larger and more prey they are messy and pigs, In the case of a ray he is normally a violent eater, messing up the substraight. You can get a skimmer but It will not deal with the amount of waste and detritus that pred tanks produce unless its a very big and effective unit (I am assuming you will be getting more preds and fish once in the new tank) so I would steer you down the ozone and UV route instead for your filtration, couple this with a wet/dry, Wc's and a good syphoning routeen and you should have a great tank.
Just my thoughts
Mike