Apple Watch upgrades are very incremental. If you buy a new one you'll very likely get software updates for longer. So I'd buy the cheapest new one you want too afford.
The always on display may not be necessary. It's mostly useful for glancing at the watch without touching it before.
The settings icon on the profile page is maybe redundant now but hardly a massive issue
I'd say, the settings icon should stay on the profile page and the tab bar should be used for some other feature. I don't change my settings so frequently that they would warrant such a prominent place.
I don't think it's useful to put an eyecatcher to a post you already read, which this icon is. I prefer that they fade to the background because they're less important.
These are the main things the 8 has over the SE:
You can actually compare all models still sold by Apple on their website.