1. Yes – it's good cover and the claims experience is good. This is important because the very last point at which you need problems with your insurance company is when you actually need them to do something.
2. Premium if you can stretch to it – IIRC it's what gets you the extended contents/accidental damage cover. This means you can claim for damage to your bike when it's outside the home, however that damage was caused (by crashing it, for instance!)
3. Your landlord should cover the buildings, so you shouldn't need to. You might want to check about liability/consequential damage though, just in case he's a cheapskate and has not thought as hard about his insurance as you have.
HTH