[TYPO3-mvc] Some random questions on how to develop with Extbase

[Fabio]

Hello mvc list,
I am kinda new with developing on Typo3 + Extbase, few times I asked for
help on this list , and always got some responses that helped me, thanks to
community for this, I hope on future when my knowledge will improve I can
help others!
Now I wanted to ask for some indications on how to handle a couple of
common development tasks on websites:

1) Guidelines, examples to read about improve performance and caching
results of Extbase complex queries. Briefly make and caching complex
queries to reduce time for quick page response
2) How to setup an Extbase extension, to make a multiform which on the end
stores data on external database and other tasks. I need to know how to
setup the controller and models for external db, the form and handle the
entire process.
3) Use  the base tt_content table, and make own basic content elements (not
custom fields, just reuse standard title, header, body fields) , to add on
backend and generate own output.

These are mainly my common important steps I do often on my works, if there
are some examples I can study it would be really helpful !
Thanks in advance
Greetings
Fabio