If we buy it are apple going to make it unupdatable in a few months
No-one knows until it happens. It was rumoured that they weren’t going to allow it to update to iOS 6 – but they did, and it slightly improved performance on my ageing 3GS. Would not be at all surprised if it won’t update to iOS 7 when that comes though. Obviously the phone won’t suddenly stop working when that happens, but eventually you won’t be able to run the latest apps.
It was a good phone at the time, but a poor quality camera and (as you say) lack of flash let it down these days IMO. In comparison to your 4 it doesn’t have a high res display and web browsing might be quite slow but it is still usable.
And, as posted above, price seems a bit steep!