First of all - welcome to the site
Secondly in response to your question, (and this is a personal response) I would tend to say yes,a base coat is a good idea. There are several ways of doing it:
1) One that has become Very popular is to use acrylic car-primer (Grey) which you should be able to pick up easily and cheaply in car accessory shops (Halfords for example)
2) The other is spray enamel. Tamiya do their own, personally I prefer the Citadel (Games Workshop) 'Chaos Black' which I find is quick-drying and covering.
The reasons for using a spray primer are twofold, firstly to give a 'key' for the top colour, secondly to check for any imperfections in the build....Cheers, Jim