No, sharks are not algae eaters, almost nothing is, unless it is starving.
What are the dimensions?
Serpae will nip in those numbers. Danios will freak the guppies out. Shark is too aggressive for guppies, two will fight to death in any tank that volume. Tetras do best in soft water; danios, sharks, guppies and most shrimp do best in neutral to hard water.
If I could give you one piece of advice, Fishy friend2 ?
YI think you need to think about what kind of fish it is that you want to keep the most, and then arrange your decor and other stocking to suit that species.
That's a better way of going about it, IME, than making lists of the things you like; unfortunatley a lot of fish just aren't compatable with many of the others.
Sorry to be askin you more stuff, but what are the dimensions of the tank? I know it's a 55 gallon, but length/width and height do have a bearing on what fish you can have