I would say from a 5, if you don’t just want a new battery, grab a Series 8/9. Keep an eye out for Black Friday deals.
Obviously a new battery is cheaper but a newer watch will get updates for much longer (duh) so that’s really between you and your wallet
If the watch is connected to your phone via Bluetooth, you can “make calls” in the same way you could make calls with any other Bluetooth accessory such as headphones or a car stereo
Text messages should just work as well, same basic idea