Welcome to AC!
Harley rasboras are fine with a shark. I'd go with a biggish group of 8-12 & maybe a pearl gourami or a trio of 1 male & 2 females...or 1 blue OR 1 gold gourami (same species, just a different color), a bit more aggressive than pearls. Call that good, most of our fish are sold as small juveniles but will reach adult size (or almost) in a year. Plan for adult size fish. Neons or cardinal tetras are too small to keep with an adult shark most times. Don't think your tank will be "magical", these are tips are based on not just my experiences but on many people's.
Have at least 2 hiding places for the shark using wood &/or rocks. You're right, sharks hate most bottom feeders or similarly shark shaped fish like Siamese algae eaters etc.
Easy plants included java fern &/or anubius attached to wood or rocks (several types of each). Cryptocorynes (many kinds) are planted in the substrate with a root tab fertilizer. Almost any light will be fine for those. Java moss is easy but it's a PITA to control, it needs lots of control. Dwarf sagitterius is a grassy type plant that's pretty easy too.
Make sure you understand the need to "cycle" your tank before adding any fish!! There's a sticky at the top of this newbie forum that explains it. It can take 6-8 weeks but it's very important for your fish!
Feel free to ask lots of questions, we'll try to help!
