Hi Carl,
1) Yes, but you'll need to download (and quite possibly buy) a GPS solution from someone else other than Google. Have a look
HERE as a few options are mentioned. You will need a fair amount of internal storage to hold the maps. Micro SD cards are cheap but so are data plans from MVNOs like Vaya or Amaysim. If I was you I'd just get a no contract data plan for the months leading up to you swapping your normal plan over. The Google maps/navigation program is very good! And it's worth having a data connection as it will give you the best route for the traffic conditions at that given time.
2) Only very few android based telephones DON'T have removable batteries so you should be fine there. From what I understand it's only really the tablets that don't often have removable batteries. If the phone you choose does have a removable battery (it probably will) you'll be able to find 1001 different replacements on the internet. If you're looking for a stock battery just get an OEM one as there are many low quality cheap and nasty batteries out there. On the other hand if you're looking for more juice there are usually high capacity options from reputable companies like Mugen power etc.
3) Yes you can easily use an external keyboard with the device. Have a look on ebay if you want a smallish keyboard.. I think you can even get them embedded into cases! They just then plug into the USB port on the device. Remember you may need an adapter if the male and female USB plugs are not the same type.
Cheers,