Whats the best way to set up CRM for a paint contractor

Whats the best way to set up CRM for a paint contractor

I run a small paint contracting company and I'm trying to get Zoho Crm set up for my process.  

I work with both commercial and residential clients.

The following is the process that normally happens in the company. 

1. Call or email comes in and an estimate appointment is scheduled. 
2. I meet with client and assess their needs.
3. I write a proposal and send it over to them. 
4. I get the job or I loose the job. 

I want to be able to keep track of all the clients that have purchased from me, and those who haven't. 
When should I convert them from a lead to a contact or account?
What about potentials? ( I don't really understand this part yet)

How should I deal with residential clients who are not part of a company? Should I create an account for them? or just a contact?

How can I easily sort clients and lost bid contacts so I can send mailing/email to only my customers?

Thanks for your help.