For something a little more robust than a free FileMaker Pro template, you could take a look at our Core2 CRM product. It handles all your basic contact management needs and quite a bit more.
For the invoiceing component you could take a look at our Core2 Invoices module.
Both solutions can be used as-is but are also sold unlocked which means you have the freedom to modify all of the code to suit your own needs. These products get you much colser to a complete and professional solution than using a free template or starting from scratch.