undergravel filters are old school and are not recommended anymore. And if your going with a SB they will not work because the sand goes through the UG filter filling the space. UG filter not a good idea.
Do some reading on sumps, IMO
the best wat to go and you will not need any HOB
filters or canister filters. Maybe only a couple PH
for flow and that is it.
Tank needs to be drilled or you can use a overflow box. If you did not buy the tank yet look at a reef ready tank. A sump also gives you a place for the heater, skimmer and other equipment to be hidden. A fuge is also a good idea to help with nitrate control. *Fuge and sump are 2 different things* They can be combined into one unit if large enough.
may help with the cycle being quicker but NSW IMO
no it will not help, bacteria grows on the surface of objects, sand, LR
, tank walls. Bacteria is not free floating and the amount you MAY get in water is not enough to justify spending $$$ on. Go with a salt mix and spend your money on a sump......
Bioballs are not needed if your using LR