How do I know whether I should use an infinitive or ...ing after adjectives?

I'm looking for a comprehensive explanation when I should use an infinitive and ...ing after adjectives and when both options are possible, what the difference is between them. Here are some example sentences to consider, but note they are only examples not the point of my question:

1. You're welcome to stay / staying here

2. I'm happy to help / helping you

3. I'm busy to do / doing housework.

4. It's funny to see / seeing everyone again

5. It's nice to meet / meeting you

6. She's stupid to give / giving up

7. I find it difficult to concentrate / concentrating.

(2) I'm happy to help you (the usual form) means 'I am glad to have the opportunity to help you'. I'm happy helping you would mean 'I feel happy while I am helping you'.

So, in general, it depends whether you are referring to the fact of doing something or the experience of doing it.

(3) definitely needs the gerund (I am busy while doing housework).

(1) and (6) need the infinitive (It is her decision to give up that is stupid, not her experience of doing so).

(4), (5) and (7) could use either. Well, if you change (5) to the past tense, we usually say It was nice to meet you when parting from a new acquaintance, but It was nice meeting you is equally acceptable if you have spent a short time in their company.