Those books are in excellent way to get started and should certainly point you in the right direction, sir.
I like your idea for the aquariums, too — the three-gallon aquarium should make a fine home for a group of colorful guppies or a fancy betta and a 30-50 gallon aquarium would work great for a couple pairs of large seahorses such as Mustangs or Sunbursts (Hippocampus erectus). The larger breeds of seahorses eat enriched frozen Mysis as their staple, everyday diet, and are therefore easier to feed than the dwarf varieties, which require copious amounts of live brine shrimp on a daily basis. (An aquarium of that size — 3050 gallons — would be a very poor choice for the tiny Pixies, since they would be all but unnoticeable in such a large volume of water, which would also make it very difficult to maintain an adequate feeding density of newly-hatched brine shrimp.)
But I can certainly give you a big thumbs up on your plans to dust off that old 30-50 gallon tank and set it up for a pair or two of large seahorses. If it’s been in storage for a while, it would be a good idea to rinse it out thoroughly with a garden hose, and then wipe down and clean the inner and outer surfaces using plain water before you fill the aquarium. If it’s an old marine aquarium, plain old kitchen-style vinegar works wonders for dried on, crusty salt deposits. Just don’t use any solvents, soaps, detergents, cleansers, glass cleaner, etc., when cleaning and refurbishing the old tank.
Best of luck with your first aquariums, sir!