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?
As for the question of whether to have your own copy of blockchain or not, it is always a personal matter. In my view, rational people, especially those concerning about privacy, security, decentralization, self-sovereignty, etc, should have their personal full nodes running. There are multiple implementations of bitcoin full node besides Bitcoin Core, so you don't necessarily need to use an "official" client for that. You can connect your mobile bitcoin wallet to your personal bitcoin full node instead of third-party servers so that a wallet provider will have a lot less information about your transactions and your real identity.