Hi @Juliey don't worry it's not a difficult process and the forum are here to help 🙂
1 - Your line is already with BT, you just need to add broadband and the calling plan to your existing BT account, your number will remain the same.
2 - All broadband packages are bundles, which means the line rental is included, you can't use the uSwitch offer though as you're already a BT customer, if you were to follow the uSwitch offer you would takeover your existing account and lose your current phone number.
3 - When BT add broadband to the existing BT line, you will also bring your calls and broadband over to BT, this will be done by BT so you don't need to contact your other provider, you have what's known as carrier pre-select for your calls, don't worry as the BT system will recognise this and take care of everything.
4 - This would depend on what broadband you order, standard (ADSL) also known as 'copper' broadband or Fibre to the cabinet (FTTC) can be done externally without anyone needing to visit your home, the down time without internet is typically 30 minutes, this is when the Openreach engineer disconnects you from your old provider to BT and carries out work at the cabinet and exchange, Fibre to the premises (FTTP) is a different process and can sometimes be a 2 stage install, the advisor will give you all the info before you commit and place the order though.
Give the same team a call on 0800 800 150, they'll guide you through it all, once done you'll have the activation date and when the broadband is switched you will need to swap your old hub to the BT provided hub.
