I'm on MFK. 300 is still overkill. Personally, I would pick a 90 for those fish, but a 75 would work fine. You have to work within people's budgets - if they're going to keep these fish, which it seems like they are, the 75 gallon would house them fine. Three loaches, four silver dollars, and a plecto could be perfectly happy. They may not be the most comfortable fish in the world, but heck, I'd be more comfortable in a mansion too, but that doesn't mean I shouldn't live in an apartment in the meantime. With proper filtration and water changes, they would be fine.
That is the thing though… in the mean time. Will the OP get an even bigger tank after they outgrow the 75-90?
Also, regardless of the overstocking, some of these fish are incompatible. Not to mention the starving frogs...
I personally don't think multiple fish upwards of a foot long will be comfortable in a 75 gallon. If you can't keep a fish totally happy, healthy, and comfortable, then why have them at all? Why put them through the stress?
Bettaloveseveryone, I really think you need to take some of those fish back to the store.