Yes, I would try to have between 2200 and 2500 gph in flow for a 75g tank. This should keep everything suspended to the water column and allow it to reach your skimmer to be removed. You should still be able to find lower flow areas for softies.
I looked at the same pumps from BRS but went with the Aqua lifter. It pumps about 3x the rate of yours. I was not as concerned with over flowing my sump if their was a malfunction. I only have about 15g of top off water at the most and my sump should hold about 12 of that. I have about 3-4 gallons of evaporation per day and it would take about 4 hours to empty my top off so at worst I would have a gallon or 2 on the floor. I do have a second float as a back up if the first one fails.
I was looking at you stand with it being completly enclosed and did not think there would be any way for the heat to escape. Are you installing fans in the stand also? If the back of the stand was open it might work better in the stand. JMO
You definitely don't want the ballasts inside the stand, moisture as you said and they will create a lot of heat. You can put them on the ground or you might look at placing them on top of your canopy until you get the other cabinet built. I would use separate reflectors for the t5 if you have room.
I can't afford a new one right now, but will keep it in mind if nothing else turns up.
I have 2 large fans blowing across the tank and one on the sump. I have 750w total light on my 120g. The 150 number came from adding in the sump volume.
I am getting 3-4 gallons of evaporation per day and it is putting too much moisture into my house. I want to see if anyone has a chiller for sale that would handle about 150g of total water volume.
Correct me if I am wrong but I thought that with Kalk you mixed it, skimmed off the top and made sure not to use what settled in the bottom? I have only used it a little, quite some time ago. I am just using 2 part daily.
Be very careful dosing iodine you can over dose and kill everything. I have heard multiple stories of this. As for the xenia mine goes through times that it does not look as good and then the next week it is back to normal and spreading like crazy.
The sump type skimmers are going to perform better. You can easily build a good sump for around $40 with buying a tank at petsmart or where ever. If you allready have a 29g tank all you need is some glass or plexiglass from home depot and a tube of aquarium grade silicone. If your tank is not drilled you will need an overflow box that would probably run you about $80-$100. Here is an easy sump design that works very well. Skimmer on the left, refugium in the middle and return pump on the right. This is a 20g tank but could be modified for a 29g.
I would try to stay away from noname lights. Most of the time you get what you pay for from ebay lighting deals. Your best deal is going to be a retro kit to save money. I think vwmike still has a 48" t5 retro that he wants to sell. you could either go with more t5's or add some mh's to it and be in great shape. I would look into hellolights they have good prices on lighting and I think that is where mike's came from.