Verbal vs de verbal vs noun

Hello
Please verify the following points.
1 * if a verb (non finite) ie verbal has an object then we either use its gerund/ infinitive, else we use its de verbalized or base noun form.

Thus we can conclude that.

Eg. 'I didn't see him playing' is an incomplete statement It's better to say- I didn't see him play.(since there is no object)
Or Complete sentence would be: I didn't see him playing football (geurnd+object)
Is that right?
2. In above sentences, word 'play' is working as a noun not as a verbAnd since "play" is one of those words which is both noun and verb we can use its base form to represent noun ie. Playbut when it comes to words which are strictly verbs like 'decide' then we have to use its gerund form with object to make any sense in the sentence
What I'm saying is:

Eg. I didn't see him play (noun)

makes sense since play is a noun as well as a verb

But I didn't see him decide is wrong because decide is not a noun thus a meaningless sentence.
Right?

3. For words which are both noun/verb do they also have deverbal noun form? If yes when would that be required if we can simply use the word(noun form) itself when noun is called for?

4. In short the i need to understand the exact rules/conventions of using verbals, de verbals and base noun(when word is both verb and noun).

Thankyou