Deans is just a better plug type than the normal mini Tamiya. Easy enough to change if your RIF doesn't come with one, but starting out its not thing to panic about.
What RIF is best for you? I'm still a noob, so take my advice as such, but I have a Specna Arms Core SA C12 which has a MOSFET and has served me pretty well for both Woodland and CQB.
Unless you have UKARA though you'll have to get a two tone. But that gun was sensibly priced (IMHO) and leaves you plenty for the rest of your kit. Don't forget a smart charger if you get LiPo batteries.
Probably best to rent for a few games to get eligible for UKARA then you can spend money on a normal colour, plus you'll know better what style of play you want to go down. You might find you don't need a hand grip, but want to get a plate carrier and pouches.
One thing I learnt the hard way is to not go cheap on the speedloaders. You'll only end up buying two or three cheap ones when you might as well have just got an Odin.