Hi mate, you don't "need" an airbrush but it really is considered an essential tool to progress. The first thing I would recommend is this site:
www.florymodels.co.uk
The info on this site is invaluable and will provide you with all the info you'll ever need. I covers absolutely all aspects of modelling, aircraft, tanks, ships, cars, sci fi, figurines etc. You can also buy videos of builds as they progress (done by Phil flory) and he covers things like airbrushing, hand painting, washing (thats for the rivets and generally dirtyfying the model).
Well worth giving it a look see and joining the forum which gives access to other members info as well.
Thank you very much for this advice. I've read the whole thread and can't wait to get started. I just need some free time...