Template Functionality

Hello,

I am considering whether I should build a WordPress website starting with a template that already contains about 50% of features that I need initially. Are there any limitations that may arise when working with templates and later on adding functionality, design tweaking, customization etc? Can a developer work through this issues without a problem? In plain English, are the templates flexible pieces of work that you can build on and on if you know the tricks?

Thank you very much for your time and response!