1.No wet dry,just a sump and a protein skimmer.LR and a sandbed wiht lots of current flowing through(About 2000gph from at least 4 different outputs) them will provide all the filtration you need.
2.PC's,They are actually more expensive than T5's or MH in many cases.Since you have a 55tall,I'd go with a single 250wMH to start off with(you can always add supllemental flourscents later on).A 250wMH can be retro'd together for about $135
3.I use 200w heaters on my tanks,the only brand i'd shy away from are those titanium heaters with the seperate thermostats(I had 2 fail)
4.Filtration for your sand?Not sure I'm following you,you can either have a shallow sand bed=SSB or a deep sand bed=DEB in your display.Both methods work great
IME,the only filtration you need is water current.You should have at least 4 outputs for water current(powerheads,return pump,etc..)