I personally use reefcleaners.org. If you are able to ship to Canada from them, it's probably the best deal. It is for me at least, but I guess it also depends on LFS.
As for snails - You want Trochus. Do not even bother with the other species unless you don't have a choice. Turbo snails do not tend to live very long. Astrea I have and have bought, but only because Trochus aren't available at my LFS and I needed something. I order Trochus online, but they are in such demand that you can only get limited amounts. I've seen them lay some eggs, but so far haven't noticed any babies(other than the ones I bought).
Ceriths aren't bad either, but mine really don't get on the rocks.
For your sand bed, conch's are awesome. Nass snails are also good, but they don't really clean the sandbed the way a conch will. I have both, and will always keep both. But the nass are more like scavengers, while the conch's will actually eat the algae and such off the surface of the sand bed. Any mixing of the sand a nass will do is really minimal.
Urchins are powerful algae eaters. 1 Urchin is like 10-20 snails in what they eat. I have 3 of them in my sump/refugium to eat algae. However, urchins also take part of the surface with them when they eat. I had painted purple rocks for example, the urchins ate the paint and turns the rock back to white. Paint didn't hurt them. But the real reason I don't put them in my DT anymore is because they got on my branching hammer coral, and they mowed down the stalks on them trying to eat algae off them. Just like the painted rock, they would take more than just the algae. One day, the tops just fell off like a tree being chopped down. So if you have any branching corals, you might skip an urchin.
Cleaner shrimp I will only keep in larger tanks. You can put them in any size tank, but IMO they irritate the coral more than anything in small tanks because they don't have many places to go. They are also food thieves. Yes in my 180g, no in my 25g and 29g tanks. Bloodshrimp is much more shy in my tank. I would personally say it is more "behaved".
I personally like hermit crabs, but beware they are extremely "rude". Some people hate them, I love them. I don't tend to buy other types of crabs.
Also, a damsel and clowns(also damsels) might not get along in a smaller tank. All of them can be territorial.