In general, you should use as few as possible.
On FireFox browser, the best privacy extension is uBlock Origin. I wouldn’t use any other extension for ad blocking or privacy unless it is for something specific you need that uBlock Origin cannot do on its own. NoScript is another privacy extension that is sometimes recommended.
There may also be some benefit to using the extension for your password manager, as it may help you identify phishing links and prevent you from filling in your password on fake or scam sites. I strongly recommend Bitwarden as a password manager.
Installing extensions is unlikely to help you defend against fingerprinting. If you are concerned about fingerprinting, then you should enable resist.fingerprint in the about:config on FireFox, or use either Tor or Mullvad Browser (which you should not install any extensions on).
trustworthy
They are recommended on privacy guides: https://www.privacyguides.org/en/search-engines/#brave-search I generally trust privacy guides, although I don’t use Brave Search.
CEO
Their CEO is anti-vax and homophobic. Brave Browser (not search) has had some controversy around including crypto, replacing ads with their own, and having had inserted affiliate links into the URL bar in the past.
censor stuff
Hard to say, the job of a search engine is to show you what you want to find.
data collection
There is telemetry that can be turned off.
AnySoftKeyboard is FOSS and supports gesture typing. It has not been updated in a while and I find it buggy.
Helium314’s OpenBoard fork is FOSS but supports Google’s proprietary gesture typing library.
FlorisBoard is FOSS and supports gesture typing, but does not have word predictions. It is being worked on.
For general use, no it is not necessary. But it depends on your threat model, or exactly how private you want to be.
I suggest looking at the pages on FireFox by Privacy Guides:
Desktop browser recommendations: https://www.privacyguides.org/en/desktop-browsers/#mullvad-leta
FireFox privacy 2021 update: https://blog.privacyguides.org/2021/12/01/firefox-privacy-2021-update/
It is FireFox that has hidden settings (about:config) adjusted for privacy. It refers to using a js file such as betterfox or arkenfox, or a pre-hardened fork of FireFox (Librewolf on desktop or Mull Browser on Android). You can improve your privacy by using a hardened FireFox, however you may also encounter more issues with website compatibility. It is a trade-off, and is usually only recommended for advanced users.
I use Heliboard: https://github.com/Helium314/HeliBoard