How can I make this rounded enclosure feasible to print?
With a couple of minor adjustments, that would print just fine standing up as it is. 

Alternatively you could lay it down with the open side facing upwards and use a few supports (my least favourite method), or simply make a flat spot on the back to lay on the printer bed. Which is probably what I would do. 

As far as shell thickness goes - 2.5 mm is pretty heavy duty. You also need to bear in mind that it's best to have a thickness as a factor of the thickness of your bead or your layer height (depends on printing orientation) - assuming you are going to print this yourself. So usually that would either be divisible by the bead width or by the layer height. If you want translucent - easy enough use translucent or clear filament. I'd probably go for 1.2 mm or 1.6 mm wall thickness.  

I made an angel at Christmas with clear PLA and quite a thick wall (wasn't my model and I didn't bother measuring - but at least 2 mm) and an LED candle lit it up really well. 

It's much easier doing this kind of thing after buying the printer. that way you learn much quicker what works and what doesn't.