There are more than a few varieties of limpets, hence why some reefers hate them and some hate them, depending on which species they encountered. For most that are sold online and are not hitchhikers, they are a fantastic addition to a CUC and they're one of my favorites! However, I wouldn't base my algae control around them, merely the biological diversity and having a fun creature.
I would not suggest sea lettuce for algae control.
How old and large is the tank. Beyond nutrient control being the most important factor, second being manual removal, the species I would add would include mexican turbo snails or urchins for large mature tanks if we're talking about hair algae. This changes if you're concerned about film algae.