I was very active in this community many years ago but I dipped after some life stuff. I need to be brought up to speed on several stuff.

1.) Does anyone even use the bitcoin q / core desktop app anymore? I remember I'd always have the whole blockchain downloaded and run the official client, but it seems that people favor "online clients" these days if that's correct terminology? Blockchain online but wallet stored on client to save room? I figure that's a must for mobile apps now?

2.) Mobile apps. Which is a good android client for bitcoin?

3.) I have lots of very old (2013) private keys generated on paper wallets from bitaddress.org with bitcoin on them. How do I go about importing them? Is there a good mobile app for importing older non-passworded private keys?

4.) Maybe I should use a desktop client to import the keys in a safe linux machine rather than android? Is there an "online" version of a desktop app so I don't have to download the whole blockchain?

5.) Is it any more or less secure using online clients vs having the blockchain fully downloaded?

I mostly tuned out of all latest updates, releases, security vulnerabilities since around 2015. Is there any news I should be up to speed on? I'm still trying to wrap my head around DeFi, NFTs, smart contracts, and all sort of new protocol lingo. Also Lighting/L1?