I am now at the point where I have a MacBook iPhone iPad and watch with the 50gb iCloud account. I’d still try to keep some aspects flexible since Apple really tries to lock you into their ecosystem as you probably know. Therefore I use Nextcloud for calendar and todos (Apple supports WebDAV quite well) and obsidian for notes, synced via Nextcloud. For photos I haven’t found a suitable alternative to iCloud sync since Apple prevents reliable background sync in other apps. In terms of benefits I would say an iPhone and MacBook give you the most synergy and everyday task coverage. I’m not really using the iPad often and don’t get much real world benefit out of the watch besides timers, current weather and the date. Mail providers all sync well via Apple mail, so I see no real reason to go for Apple here. For passwords, the Apple system is more convenient but you also need an Apple device around (or Apple software on windows). For this I went with KeepassXC since it’s open source and runs on everything. The KeePassium app works well on iOS and integrates with the password dialogue. I sync my password database via Nextcloud.

So my personal opinion is: Apple is nice and useful but I try to keep some freedom from their sometimes erratic policies. With my current setup I feel like I can switch away from Apple quite fast. I hope this helps a bit for perspective.