Hi there, first off - welcome to the forums!
Congratulations on your desire to serve proper draft beer, few care enough to be sure that it's done right and by posting here you've already shown that you have what it takes!
For your situation and climate, there is no substitute for the two tap high-capacity, 120' coil, dual tap jockey-box.
I have used several of these built by MM and others, and also build many myself.
If you have the hole saw and appropriate measuring and assembly skills, then you can save a little dough if you get your cooler locally and assemble the box yourself, the shopping list is easy, buy all the parts you need (MM lists "replacement parts" as a tab on the item). If not, buy it directly from MM, when you price it all out, you only save about $40 or so, depending on what parts you decide to go with...
I now build out all jockey boxes with stainless steel faucet shanks and SS faucets as well. I'm sure that MM would add these to your order for the difference in price if you want to buy a pre-assembled unit.
You will save money on ice by having the dual tap, as you don't have to feed ice to two coolers, and the 120' coils never disappoint. Going with anything less, in the heat that you face, will just be cause for aggravation.
Good luck!
Also, if you know what temperature your kegs will average, you can build some nice LONG jumper lines of 3/16" to restrict the flow down from the high amount of pressure you will need to keep your beer properly carbonated...though at temps that high, quick consumption is probably a must!
BTW - a cold plate style jockey box, though cheaper, will NEVER be suitable to cool beer for the environs you describe. Cold plates are only suitable for achieving proper dispense temp when you can keep the keg under 55 deg. F and your dispense needs are sporadic.
If you absolutely must build two separate boxes, go with the 120', one in each cooler, this will only cost you the price of the additional cooler and time, and I would suggest mounting one cooler with a left hand coil and one with a right hand coil in case you decide in the future to make a single cooler dual-tap unit.
I really recommend if you've never done this before that you you buy the pre-assembled unit, however, if you want to get industrious...
You will need the following:
1 48qt cooler, think carefully about whether to purchase a cooler with a bottom mounted plug drain or not - these are notorious for leaking, which is fine on the sidelines of the soccer field, but is not fine over the 100% ginkgo hardwood floor at an upscale venue... recommend you build boxes from 48qt Coleman or Igloo coolers with no bottom drain, and then cart off and drain at teardown.
Two 120' Stainless steel Coils
Ice-Box Shanks for the back (where beer goes in)
SS Faucet Shanks
SS Faucets
2 x Jumper Hoses
2 x SS Beer couplers (7485E-S are economical)
12 feet of Gas line (2 x 6' CO2 Line - I make all gas lines for boxes 6' now...)
1 CO2 Regulator (642-2 or equivalent - single reg with two way manifold, etc...)
1 5lb (or larger?) CO2 bottle.
Appropriate Oetiker stepless clamps to ensure all connections are tight.