I think you need a number of related tables, but you also describe two tables I'd combine into a single table. Ever have a vendor turn around and be a customer? It's not the best approach to use records in two different tables to document contact information in cases where a vendor is also a customer. Plus, contact info requires much the same interface for an individual whether they be vendor, customer or both--so using one table for all contacts of both types allows you to more easily create and maintain a single layout for entering/editing/viewing contact info. You can add a type field to use to identify the contact type.
I don't know your business but your reference to "equipment specs" suggests that you will also need a table for equipment specs that you can link to a customer contact so that you can more easily service more than one piece of equipment for a given customer. Likewise, your vendors probably supply more than one item to your business so a table listing each product supplied by a vendor--plus tables for purchase orders and purchase order line items will likely be useful. In addition, unless the servicing you perform for each customer is very simple, you will likely need a related table of work order line items where you identify the equipment serviced, the service performed and any additional details such as number of billedhours, etc. so that your work order can produce a flexible, itemized list of the work performed.
The White Paper for FMP Novices is useful
Lynda dot com has Filemaker Videos (portions are free)
A free calendar is available to be bolted onto your database
You can search specific Filemaker sites on this Custom Google Search
Looking at FMP business database demos is useful - some are fully useable
The Excelisys Business Tracker V3.0
Filemaker released a FMP runtime database in 2007 for students called "Campus Productivity Kit" and is available online, noteably at CNet
Google "Campus Productivity Kit"
The Computer Guy, Seattle