An NIE is like a tax identifier .... you need it to do lots of things over here. If someone issues you an invoice they need your NIE, banks normally need them to open accounts. You can get them from the Spanish Embassy in the UK, or over here at your local Police station normally. See forms download above.

You dont say if you are of retirement age or not regarding healthcare. Normally you will get an E106 document from DWP Newcastle overseas medical benefits section. You will use this in Spain to get up to two years free State healthcare. After that if either you or your partner are of pensionable age you replace it with an E121. If you work, you are contributing to the spanish system so you qualify. If you dont work and you are not of pensionable age then you normally wont get any health cover and have to go private