I think 6-8 frogs is a good number to keep in that size of aquarium safely. Technically the tank could support a few more but the more frogs you keep together the greater your risk of infections such as red leg increase.
I don't have much experience with fresh water sumps or as they're also called 'refugiums'. I have read about them and they do seem neat, they do increase your water volume but I do not think they really make up for good bio/mech filtration that a canister filter gives you. My Eheim Classic filter is probably one single best product I've ever purchased for my aquarium so I guess we will have to agree to disagree on filtration.
The care for these variations of xenopus are all the same, but yes you could mix it up if you were able to locate a supplier of the more rare types.
Xenopus.com? Yes they do sell pellets for these animals, I've never really read a review of this food. I would assume it is of high quality, the site mainly seems to sell xenopus as lab animals, kind of pricey but may very well be worth it if you desire rare pigmented frogs.
Reptomin is really not considered a high quality pellet food -however- it seems to be a great staple for african clawed frogs. Some may disagree, but I've never heard of an ACF owner who had an issue with reptomin as a staple. It does have high protein but the phosphorus / calcium ratio is a bit poor.. I think supplementing earthworms would make up for this deficiency. May want to skip the red wrigglers and go straight for canadian nightcrawlers. For one red wrigglers are a bit less palatable (though I doubt a xenopus would care.. most frogs do) and there seems to be some talk that red wrigglers may be a bit toxic (at least to garter snakes). I'd play it safe, eventually your frogs become so large they will prefer the larger canadian nightcrawlers anyways, and if you buy from a bait store or walmart, they cost the same anyways.
Sub-adults should be fed daily, adults should be fed 3-4 times a week. You're absolutely right, if fed daily they become quite fat. Then again it also depends on how much you feed them, if you fed them a little bit each day, that would be fine. My feeding regimen is one canadian nightcrawler each, every other day, some days I skip the earthworms and feed reptomin, so roughly 3 earthworms and 1 reptomin feeding, per week. Crickets are also given as treats, usually on reptomin days (worms make fat, stuffed frogs).
Yes
Yes, but be wary of plastic plants. They can easily cut the delicate webbing of their feet. Go silk or real plants.
I would argue this site is correct. Real plants help add additional biofiltration, improve water quality, and create a more natural habitat.
Not really. Their plant destroying prowess is a bit overrated. True nightmares to planted tanks would be turtles, goldfish, cichlids, ect...
My ACF tank has jungle vals, bacopa, moss, water sprite, wisteria, duckweed, and frog bit and it all grows just fine they hardly if ever kick up anything.
My best advice here and what is more beneficial for your frogs, get water sprite (indian fern, there are several varieties of this plant). Skip the fake stuff, floating plants such as this are fantastic, grow quickly, keep your nitrates under control and have some superb advantages..
For starters floating plants have one HUGE overlooked benefit, it makes frogs less prone to escaping. They provide a general feeling of security to the frog (froggy thought: predators can't see me! I have these plants hiding me!). They give the frog the ability to bask, watch them at night, they will use water sprite to rest -- with their nose above the water. Think how nice it is for them, an aquatic air breathing animal to have the ability to rest, breathe, relax..
I don't see why not.