hi Titch and welcome to the forum.
If you don't live in Fethiye you will need to find out which Passport Police you will need to use, ie, Dalyan, Kalkan, Kas etc don't come under Fethiye's jurisdiction, though I believe Gocek does.
Also, if you don't have enough funds to show in your savings account in Turkey, you can show evidence of a monthly income to a UK bank account, but you will need to have your bank statements translated, by a certified translator.
Also, whilst you can take back your passport before your Residency is completed, I'd double check if I were you, to make sure that this doesn't stop the process, as I understood that if you take your passport back, you will have to start everything again, including the payment, next time you're back in Turkey.