A lot of that is down to personal choice.
Personally I dont like plastic hard tubing as there is a greater risk of leaks at the fittings because you are relying entirely on o rings to do their job. Technically you are doing the same with any rotary fittings too along with all of the blocks. There is also the brittle issue with acrylic and the coolant compatibility of petg. Soft tubing is far easier to route and dismantle but obviously doesn't have the same look.
Integrated pump reservoirs are fine but some can exhibit more noise through the mountings. Separating the two allows you to easily isolate the pump using foam or a shogee sandwich.
Coolant choice will depend on tubing choice as there are incompatibilities with glycol and insome cases particulate matter. Personally, I preferred to use the tried and tested OAT based coolant from my car. If it's good enough to prevent corrosion with aluminium, cast iron, steel, brass and copper for over 20 years, and do it's job of keeping an engine cool, it's good enough for my pc. I've been running this mix (1:4) of antifreeze concentrate and DI water for 4 years without a problem. Only thing is that ethylene glycol which is the main chemical in the concentrate is toxic, fairly viscous (thick) and incompatible with some tubing. Most others will recommend using mayhems, xspc or ek or even plain DI water with a silver coil or biocide.
Leds are great. Makes no difference to the performance but it's all about aesthetics these days so go as nuts as you like.