The Ice Cap pendants are nice, but the Lumenarcs give you a broader coverage area... They are both on the high end in terms of quality, so you should be good no matter which direction you decide to go in...
Moguls Vs DE you could debate till you're blue in the face... A lot depends on what bulb you are wanting to run, and which color spectrum you are trying to achieve... There is a big difference between a 10k Current bulb and a 10k Hamilton bulb... As well as a 14k Phoenix and 12k Reeflux...
t5's seem to be the latest and greatest thing... They use less energy and last longer... You need to buy individual reflectors with t5's though... VHO's have internal reflectors... A lot of people prefer the look of VHO actinics over t5 actinics... They say the colors "pop" more under VHO's...
I know a lot of people that run pond pumps as their returns... 3600 gph shouldn't be too much... So long as your return rate doesn't exceed your overflows rate of drain to the sump you're fine... If you have too fast of a return pump, you can pump all the water from your sump into your display tank before it has a chance to drain and there by overflowing your display tank all over the floor...
Restricting the output on the pump isn't really the best thing for the pump... It tends to shorten the life of the pump and can increase the heat output...
Stuck heaters can be a problem... The way to get around it is by using a full aquarium controller (Neptune, Reefkeeper, etc) as Garry suggested, or buy purchasing a temperature controller (less expensive but only controls temp)... Controllers can keep your tank's temperature more consistant... They turn on/off within .1 or .2 degrees, if you depend on the on/off switch in a heater there can be a 1 to 2 degree difference...
You'll need more flow in your tank besides 2 koralias... But it doesn't all have to come at once... You can add more PH's as you increase your bioload... Circulation is important to carry food/nutrients to your corals, and to keep extra nutrients/poop in the water column so that your skimmer can take it out... If the nutrients/poop has a chance to settle, it can increase ammonia/nitrites/nitrates/phosphates in your water...
IMO the SeaClone is an inferior product... There are many other manufacturers that put out more efficient skimmers... Bubble king is up there in terms of quality, but it all depends on how much you are wanting to spend and what type of skimmer you are wanting... The main types of skimmers are Beckett, Down Draft, and Venturi skimmers... There are pros and cons to all... And there is a wide difference between the best and worst Venturi skimmers...