Contact, lead, deal

Contact, lead, deal

We are a small company B2C that conciders Zoho CRM. It needs to be scaled down to be useful.
We are intending to import the customer data we have into contacts, i.e from old customers, we have a high level of repeat business. A couple of questions:
1. If we recevie a call we dont know if it's a new or an existing customer (we would look into integrate the phone sysetm at one point). The obvious is to start entering the call into a lead but I find no way how to recognize the customer if it exists in Contacts? Any suggestions?
2. If it's a repeat customer, i.e existing in Contacts, what should I do then, I would have thought I could turn it into a new lead but find no way to do that? I've seen somewhere you could turn it into a new deal but do not find a way.
3. I see little use of Accounts in our business setup as we are talking B2C - anyone disagre with that, if so why?
4. When creating a lead I would always like to enter this person into contacts in order to cath him/her in our campaigns but there seem to be a lot of different definitions in leads and contacts. I've played around trying to figure out how to align. Any tips here how to do this effeciently and securely?
5. When setting up and tailor the the setup for one staff, is there an easy way to copy that setup to other new staff when setting it up?

Lots of questions, there are more but would be grateful for any respons on above first.

Best regards from a cold Sweden