Punk as a canal boat builder i can speak with reasonable authority.
Initial purchase, plus survey costs for piece of mind and costs to fix anything the survey brings up. Craning and dry dock costs maybe. Canal boats have a system like an MOT to ensure safety, so the boat has to reach a minimum standard should be meet by the seller.
OK, wide beam obviously has more space, fine if you stay on the river but once you get onto the canal system you can be limited by lock sizes.
Yes you have to pay a license to CRT, usually done on length, might be more to cruise on the Themes.
No mooring, thats fine for the moment, there are rumours that you may have to get a permanent mooring soon, don't know. BUT that will be thousands if introduced.
Other costs, fuel - diesel is cheaper for domestic use more expensive for moving the boat, you have to declare at point of purchase.
Coal - for heating it does cost, or wood if you can get it cheaper.
Pump outs - depends on the boats system but expect to pay to get rid of it.
Fines - if you don't move every 2 weeks you can get fined.
Access bear it in mind you might have to leave the bike a mile up the towpath, depending on where you moor.
Thats it for now.
Nick