A few questions & advice

[Mcjoint]

first grow, i have a 30"x18"x6' space to work with. i am going to be scrogging in dwc, i am planing on using a 13 gallon cooler with plants in it, green crack and skunk 47. i will also be using a smaller peltier water chiller to help keep the temps down in the res. i have a 6" fan on a variable speed switch and carbon filter on the outside of the space. in side the space there is a small oscillating fan to help push air around. i will be using a mar hydro 300 (150 true watt) and an ebay mars hydro knock off also 150 true watt.currently with only the mars hydro on temps are reaching a high 0f 79. when i add the second light my temps will get higher. my questions is how hot can my space get as long as i maintain the water at 68ish degrees?
i am currently have my lights on during the day, i plan on slowly move them into a night schedule however, i know my temps still might still get alittle hot. i would also like to try using the gas lantern routine (12-1 light schedule) to also help keep temps a little lower and save some coin. my question is can i already start to slowing change my 7 day old seedlings to that schedule?
for food i am gonna be using GH flore 3 series and calimag, i will be using ro water and hydroguard.
is foliar feeding recommended? if so can i use the GH feed at half strength or there something else i should be using? critics welcome
i would love to add a dedicated a/c unit but i can't do to space.

 

[Papageno]

Proper temps are on this chart. Don't go above high 80's without CO2. Try to keep it closer to the 70's and low 80's with lights on. During bloom, if you have the right genetics, letting it get real cool at night will stimulate dark coloring like deep reds and purples. I got a plant now with sugar leaves so dark they almost look black.

This is behind HPS glasses under HPS lighting so not very clear or accurate but you get the point... Under LEDS you can get even better coloring.