Have you actually been told this by your consultant or DSN? If your consultant thinks you are suitable for a pump the choice will be limited by what pumps are supported by your hospital pump clinic.
Whether it's water proof or not depends on the pump. The Medtronic 640 is. the Animas vibe might be? For not waterproof pumps you disconnect - you don't take out the cannula you just disconnect the tubing feeding insulin into the cannula and, if I were getting in a pool I'd put a stopper connector on to close the cannula.
Cannulas are inserted by various mechanisms with various needle lengths. Some pumps have more choices than others.
You take it off by pulling the cannula out. It's just ripping off a plaster. Occasionally there might be little bumps/scars for a day or two after taking a cannula out. You deal with this by good site rotation, changing cannula sites every 3 days.
You just sleep with it. You could get a pump belt or tuck it in pj pocket or just let it follow you round the bed.
Why would a pump wake you if you were extremely low? A pump just delivers insulin. They don't monitor your blood sugar unless you are also wearing a continuous glucose monitor. If your basal rate is set correctly on your pump you shouldn't be waking extremely low.
The pump automatically delivers your basal insulin. You need to press buttons to deliver bolus insulin. There are automatic "artificial pancreases" being developed with Medtronic 670 launched in the us and Oxford workin on algorithms to automate the 640.
Pumps need a bit off training and a bit of understanding to use. John Walsh's book "pumping insulin" is a good user guide to understand how pumps work.
Pumps are expensive, around £3,000 +. They aren't easy to break and most are warranted for 4years. It's unusual for pumps to be self funded in the uk because they won't be sold to you unless you are going to be under the care of a HCP teaching you how to use it, and if your NHS pump clinic is going to do that they might as well just pay for the pump. It is recommended that insulin pumps are insured and even if you're an NHS patient with a funded pump it's your reponsibiity to insure it, this can be covered by content insurance or special insulin pump insurance for about £7 a month.