I'm not in a good position to compare the relative merits of consumer ISPs, as my ISP has more of a business focus. However, I'm sure that others will encourage you to compare Plusnet's Fibre Unlimited to BT Infinity, also Sky's fibre products (especially if you are already a Sky customer). I can say that your Newnet product sounds expensive - I pay around double what you pay for 80/20 Fibre to the Cabinet with a 100GB/month download allowance and a routed IP block. You can get low usage ADSL products for under £10/month in many areas that have more than a 10GB/month usage allowance.
So far as your e-mail address goes, I would establish an ISP independent e-mail address now and start notifying people of your new address. This will make your eventual change of ISP easier when you decide to move. If you're prepared to pay a little, the 'gold standard' is to register a domain and pay for hosted mail service on it (make sure if you do this that the domain is registered to you, so that you can transfer it away if necessary). If you want something free, try Gmail, Yahoo! or outlook.com (the Hotmail replacement).