this one is gonna be a doozy! thank god i type fast...
ok...here is the layout i would suggest. i still don't know where the door really is; where the "niche" is; where closets and windows are; etc...
ok, now the fun begins.
Cooling
with 4,000w of light you are going to need an a/c unless you live in the antarctic. doesn't matter how much you push air through thouse lights. your options are a portable a/c which is very inefficient and will have to be vented into the attic or out a window. a window a/c which is efficient but has to sit in a window. a minisplit which is expensive but the most efficient way to cool the room. the compressor can be put on the roof or hidden behind shrubs in the yard somewhere.
depending on the size of the a/c you get will also determine the options you have for venting your lights. if your a/c is big enough (24,000btu+) then you can run your lights in bat wing reflectors and you won't need any inline fans. if you can vent your hoods into the attic then you won't need that big of an a/c (12,000btu). should you decide to air cool your lights you will have 2 options. to pull air from outside of the room (the attic or a window) and then vent that air back outside of the room. this way you really have no odor issues. if you go the other route and pull air from the room through your lights then you will need to pass that air trough a carbon filter before exhausting it out of the room. you could put a small carbon filter on the opening of both rows of lights and then filter the air going through the hoods. this will keep your hoods and bulbs clean and will also take away the need for a seperate fan and carbon filter in the room. you could probably get away without doing this but then you would need a large carbon filter in the room on a 10-12" fan running nonstop during flowering; you'd want to turn the air over every minute or less.
System
based on how big you said you wanted to run your plants i would think 16 plants would be perfect for 4,000w. if you 18 or 24 then you just need to run smaller plants in a tighter area. probably no training like LST or Supercropping. maybe TOP once or twice. problem with most ebb and grow systems is that the reservoir, control bucket, grow sites, and tubing heat up when they are sitting under those hot lights. so between feeding the water heats up and then when the pump comes on it shocks the roots with hot water. you have a chiller so your reservoir will be cold but not the standing water in the buckets, tubing, and control bucket. this hot water leads to algae and slime issues which create problems in your reservoir. with the CAP system it is best to put some planks or something under the grow buckets to raise them 1-2" above the control bucket. this helps to drain the tubing and grow buckets better. it also helps to use a small wedge (1/2") to tilt the grow buckets to the drain side. this will get most of the water out of the buckets so that your roots aren't sitting in warm water when the plant gets bigger. the only way i know to keep the control bucket cool is to keep it outside of the room or in a dark closet. not sure if this is an option for you.
both the sentinel and titan system are more efficient and their buckets drain better but you will have the same issues in the control bucket ans tubing. one way i have found that helps keep your system clean is to run and enzyme product like aquashield, sensizyme, or hyfgrozyme. some guys even run small doses of hydrogen peroxide (h2o2). changing your reservoir weekly will also help. if you have the time then flush your system with water during this change. fill the reservoir with fresh water and fill/drain in a few times before dumping that water and adding fresh water and nutes. after every harvest tear your system down and clean everything. the bucket, tubing, reservoir, and control bucket. helps to let your tubing sit in a bucket of diluted bleach and then rinse them out.
you mention you have a 75 gallon reservoir. i think you meant a 50 gallons reservoir. the CAP system comes with a 50 gallon reservour and the only 70 gallon reservoirs i have ever seen are large rectangular ones for flood tables. you will not need to fill the res all the way; especially during veg and early flower. fill your buckets with hydroton and then add water to your system. run the pump to fill the buckets and then slowly keep adding just enough water till all the buckets are full and the float valve shuts off the flood pump. you want about 10 gallons in your reservoir with all of the buckets full. then drain the buckets back into the reservoir and you will see how much water you need. as you get into flower and the palnts get bigger you will notice you need more water in the reservoir as they are drinking more. it will take some tweaking but you will get it figured out over time. with 24 plants i can tell you that you will never need more than 40 gallons of water in your reservoir and you can do less if you want to tap off your well in the middle of the week. having 50 gallons in your res with a bunch of small plants is just a waste of nutes.
Chiller
a 2hp chiller is a sizeable unit. problem is you are using it wrong. a 1/2hp unit would be just fine to cool your reservoir. you said you keep your reservoir at 67 degrees. shoot for 64 if you can. you are not supposed to run nutrient water through your chiller. it will ruin the internal coils of the condenser and also cause issues with your pH and ppm of your nnutrient solution. chillers are meant to be run on their own reservoir. with a unit like that you would be best off getting a small 20-30 gallon reservoir and using that as your chiller reservoir. use a pump to run water to your chiller and then have it drain back into your reservoir. then use a submersible pump to pull water from that reservoir and pump it through a cool coil or wort coil that sits in your reservoir. i prefer the wort coils. this way you are not mizing nutrients with the water going through your chiller. you also don't want to keep your chiller in your grow room if you can avoid it. they emmit heat. if your ac can handle it then fine but it;s best to be kept outside of the room like the commercial units or the window units.
Electrical
what you described sounds good. run your lights off the controller. then bring in a 30 amp 120v line to run your outlets for fans and stuff. use #10 wire. then, depending on your a/c situation and dehumidifier you will probably have to bring in another line fo them. 30 amp 120v.
that's all i got so far. lol