Congrats and welcome! The AW IMR 14500's are good-performing batteries with a low-res atty. A lot of folks like the Cisco LR atomizers from avidvaper.com - I happen to prefer the 306's to the 510's, but it's all in what works best for you. Ikenvape is another good source of high-quality atomizers, but I believe he is still waiting for new stock. I've had good luck with atomizers from either site, and like that they aren't filled with nasty primer. For 306's, the drip tips that are sold on the reosmods site are a nice size - they're 1/4" longer than "standard", and therefore feel a little cooler. The translucent tips at avidvaper are the same length. I happen to prefer the solid delrin tips, but a translucent one may be a good option to start with if you go the 306 route, as you can see the juice in the atty.
901's are a little tricker, since they have the air-hole in the side. Rob includes an o-ring in the package that can be used to catch wayward juice. He has a couple of tutorial videos on his site, one of which illustrates how to use the o-ring. I haven't used a 510 carto with my REO's yet, but there is another thread here discussing carto use.
Thinner juices (higher % of PG) may require the use of the reducer tube that will come with your Mini. It is just a short piece of skinny tubing that fits inside of the feed tube. It keeps thinner juices from "self-feeding". I use Halo Menthol Ice in one of my Mini's and use the reducer tube in that one, and it works great. Thicker VG-based juices shouldn't need the reducer tube.
When "squonking" (this is the term given to squeezing the bottle by our beloved Jack Murray), quit as soon as you see any juice in the reservoir. That juice will get sucked back into the atty when you take a drag. Another method has been used with great success, called "blind squonking". Suck on the atomizer while squeezing the bottle, and stop as soon as you feel any resistance, or hear any gurgling. It's a good method to use when you can't look to see what you are doing, and quickly becomes second-nature. A dry atty will need to be properly primed with juice before using, just like with any device.
Best of luck - hope you enjoy your Mini!