I also wish to warn about mixing a redtail shark with huhli loaches, especially in that size of a tank. The shark will eventually eat the loaches.
Redtail sharks average 6 - 8 inches full grown and are aggressive and territorial. I have one in a 40 gallon tank by himself because he tolerates no tankmates, and he's still only about 5 inches right now.
Mixing the shark with the rainbows would depend on which rainbows you got, and how soon you intended to upgrade to a larger tank. I wouldn't advise anything less than 55 - 75 gallons for the shark as it becomes full grown.
Also be forewarned, most of the rainbows will eat many of the different types of aquarium plants, as will a bristlnose pleco.
Have you considered gouramis and/or tetras? Livebearers? Botia loaches? killiefish? hatchetfish? dwarf cichlids?
That size of a tank would be an awesome place for a few pairs of dwarf cichlids, some cory cats or botia loaches, and for algae eater, maybe some otocinclus, which would eat the algae, leave the plants alone, and not outgrow the tank.
Picture a pair of these:
Apistogramma bitaeniata (this is a pic of the male)
a pair of these:
Apistogramma borellii (pic of the male)
and/or a pair of these (depending on how dense the planting and provision for territory):
Pelvicachromis pulcher AKA Kribensis (pic is of the male)
You could do a lot with that tank for color, activity levels, and etc... but you'd be a bit more limited on tankmates for the dwarf cichlids. Botia loaches can still work, as can small plecos like the pitbull pleco
If you consider the dwarf cichlids, be sure you are matching their pH needs. They prefer softer water, as does the pitbull pleco. There are also cory cats that do well in the softer water, and are colorful, like the cory sterbai
As for the SAE's... be careful what you put those with, they can be very aggressive. There are 2 species of fish that are ALMOST identical, but very different in aggression levels and eating habits. I will check with my husband about the name of the other, as I can't seem to remember it right now, even though I can picture the fish in my head just fine. (it's been a long day) But, many LFS's sell them both as SAE's... if you don't know how to tell the difference, you could have quite a mess on your hands. (I hope I am interpreting the initials correctly in SAE meaning siamese algae eater, aka, tai flying fox?) There is another called the chinese algae eater, and those get really aggressive as they mature, and will attack fish.
I'm going to bed now, but let me know if you need more help, I'll be around tomorrow during the day for a little while.