Hi, starting off with the m4 family is a good move. However, I would suggest that CYMA isn't the best brand to start off with unless you are are planning (and willing) to 'upgrade' it along the way... Not to say it will break down straight away but QC won't be as stringent as other brands such as G&G or G&P. The benefits is that parts will be Tokyo Marui compatible and the outlay will be less than the other 2 brands.
I started off with a G&G Combat machine and although it has a plastic body, you couldnt tell from looking at it and it was tough material! Also, there has been times I would miss the lighter weight in longer games compared to full metal rifles. G&G also have their top tech range if you up your budget, these will have full metal bodies and it will come with quite a few upgrades already, such as a decent high torque motor, tightbore barrel, upgraded wiring and more recently in their Gen 3 range, a MOSFET. A handy feature that is present in G&G m4's is the easy spring realese which relaxes the spring when storing. Their blowback feature is nice but hardly essential in my opinion however.
G&P do make very nice looking and high quality m4's. Definitely comparable to G&G although they don't feature blowback nor have the spring release button that G&G does however. One thing I would mention about them that annoys me is that their barrels have a postive thread which is against the grain for the majority of other companies. This means that a majority of third party flash hiders/suppressors will not fit unless you buy an adaptor to convert it to a negative thread.