What do you usually do with bugs an dfish you've caught and already donated to the museum?

So it depends if Nook's is open. I got the gold nugget island last week, and had a bunch of scorpions when I got back. Nook's was closed, so I put it in my storage, and just waited until Flick came by today. Otherwise, I usually sell to Nook's the day I catch it.

It depends. High value bugs/fish? Maybe worth saving for the bonus if there's a lot. Like big fish island or tarantula/scorpian island a lot. Average to low value? Sell to nooklings. The greater the quantity and higher sell value makes waiting more worth it but even then it's a wash in my opinion.

You're better off just immediately having the bells considering most of what you may spend it on rotates daily (high dollar nooklings items). Unless you need nothing immediately, in which case you don't need bells anyway. Bells are so easy to get that you don't really get much in the long run by hording.

By numbers you'll make more if you wait, but if it's the difference between waiting a week to make 300,000 bells or just selling immediately and making 200,000 bells it really doesn't matter. You can make 100,000 in a day or two without even considering turnips, so to me it's pretty negligible.

I never even saw CJ until quite late. I just sold them all at Nook's. I still do that but I'll try and save 3 to make a statue.

Save 3 of each for models and sell the rest. 300k is nothing.