If you're just a casual user then yeah, you can consider a battery replacement and skip the upgrade till you really need to, but the upgrades of the iPhone 13 Pro Max over the XS Max are huge in almost all aspects. Definitely can give it a go if you have the financial means.

My wife same. After the event first thing she asked me was "So? When gonna buy 13 Pro Max?"
The pro-motion thingy is the 120hz refresh rate bro

iPhone restoration is pretty flawless but ya, it is troublesome especially if you have lots of data and you're doing it over iTunes.

I'm looking to see how iOS 15 will run on my iPhone 6S. Passing it on to my mum to replace her 5S. It's still good and working - and Apple still provides security updates for it occasionally but it's unbearably slow now. Takes 3 to 5 seconds to launch apps now, hahaha...

1. Any good and reliable 20W USB-C PD charger will do.

2. Depending on budget you can get those cap ayam RM5 ones from some sellers on Shopee, or you can get the midrange ones like Blue-O, Nillkin, etc, or if you wanna splurge you can go for brands like hoda,  flolab, etc.
Ya, the new video shooting capabilities are pretty much useless to me too

Well, my 6S runs pretty great on iOS 14 - probably also because the battery is a new one and still at 100% capacity. We'll see - few hours to go before iOS 15 is ready for download!