I use ZOHO to track two types of businesses - completely different

So I have in database full mixture of Accounts and Contacts

I differentiate only Potentials by Service type, so one business have 1 Service type and second business have 2 Service type.

I have two questions:

1. How to filter contacts connected with only 1 Service type? - I want to do mailing to this group

2. For future - how to differentiate Leads/Accounts while enter to CRM and have 2 groups connected with specific business?

Thank you for your help

Paweł