Im wondering what order i'm suppose to watch them. I watched unlimited blade works, but there was no real ending? Is there a more after, or is it just left up to the imagination as to what happens to caster.

the whole show is fanservice
you should just watch the series you want.

It's all subjective opinion but I'd start off with Fate Zero (currently available on Netflix) then check into the first season of UBW. Unlimited Blade Works isn't over, the first season is and the second should pick up soon enough. I'm convinced Fate Zero (10 years prior to F/SN) is going to end up being the best though.

Currently watching the older Fate/Stay Night and it's... laughable.

Is a visual novel with plus route ^^

don't watch it. Shit show. Waste of time.

The manga is set after the first series isn't it??