Yep, should be ok. No more than three though. Trios (I male, 2 female) work best for gouramis to minimise aggression. But its important for them to be able to have their on territories and places they can hide from each other if need be - so don't let your tank be too bare. They really like having lots of plants, especially floating ones, though not absolutely necessary. Any filter should be fine really, as long as it doesn't create too strong a current, gouramis prefer calmer water.
I don't know anything about weather loaches but cories are fine. You might want to get a larger group of cories (4-6) they are happiest in groups. You might like to get a small group of colourful fish that swim at midlevel, some docile tetras or something. You should have the room, provided your filtration is adequate for the size tank. Be careful, make sure any you pick aren't fin nippers, they might go after yout gouramis fins. In my 39 gallon with my pearl trio I keep cories, cardinal tetras, platies and a bristlenose, no probs.
Hope everything goes well for you - pearls are a beautiful fish, you've made a good choice!

Just be careful you're sexing them right when you go get them (its often more difficult when they're smaller and younger in LFS's) to save later drama.
*Edit* Just wanted to add, not sure how new to fishkeeping you are, but make sure you cycle your tank properly! If you don't know what I'm talking about, see the beginner's forum. Or, if you're cloning, or getting used filter media, it might be wise to not overdo it and only add a few fish at a time. E.g. your gouramis, then a few weeks later your cories...or vice versa, etc. Actually it's never the best idea to fully stock a tank at once, anyway.