The compatability factor looks good. Here is a chart that I reference all the time. http://www.liveaquaria.com/general/f...lity_chart.cfm
I think it will be a bit overstocked though. If you follow the 1 inch of fish per gallon rule, you will have 15 inches of fish in a 5 gallon (3 inches each loach x 3, 2 inches of betta, 1.5 x3 goldens) which is really overstocked. BUT- I am someone with an overstocked tank, so I don't want to be a hypocrite. It takes research as far as where they will be in the tank (top-middle-bottom). Having a bio-wheel helps with the bio-load, but be prepared for regular water testing and water changes without fail. You really need to make a commitment to stay on top of it and be sure you are prepared to immediately remedy anything that might come up. With a small tank you can't sit on it for a day or two while you figure it out, because it will go downhill fast.
From what I understand loaches are supposed to be in groups of 2 or more, at least if you ever want to see them come out of hiding. I'm also under the impression that loaches need a lot of swimming room and I don't know if 5 gallons will be enough for them, but if you really love
loaches I understand the desire for them. Make sure you have plenty of hiding spots (like the plants). Also they are not known to be a hardy fish for cycling, so don't add them until the tank cycles.
I do think the loaches with a dark male betta and the golden white clouds will be a beautiful display! Maybe do 2 loaches and 3 white clouds since they stay small. I would start the cycle with just the white clouds though, they are very hardy and don't seem to mind when others get added to their tank. Once cycled, then add the betta, and lastly after your bioload adjusts to the new fish, add the loaches.
When it's all set up with fish post a photo, it sounds like it's going to look great!