Used both since 2000, it's easier to get used to with the 7's for a new user due to the two eye/same image similarity to normal human eyesight. There are tactical benefits to a single 14, and more for dual 14's, but unless you are putting your life on the line, I couldn't justify the money.
This is good advice. But I highly recommend trying 7's before investing in them.
Make sure that the objective focus and diopter focus are correctly set. On most units, one is on the objective end, and one is on the viewer's end.
Use them with both eyes open. You'll get used to it so that your brain meshes the details from each image together well.
Yep, that's what I said. It gets better over time, trust me. You just need to practice with them, they take getting used to. Both eyes open for sure, and put it over your non-dominant eye. You need to mount them to your head and stop holding it. Get used to walking like normal. Don't look down, look straight ahead.
TNVC can square you away on gear and they're reputable and will go over options and keep you in your budget if need be. It's who I go through when possible. Stellar CS too.
The below is just extra ideas:
You can get the dual 14 setup but I think a set of 15's w/matched WP tubes would better. You keep some depth perception and this is how to go with binocular NODs. More expensive for sure, but that's one of the pairs I'd like someday, an aviation grade set in a tougher housing. Unless you've got the cash to burn on that, I think a pair of 14's, one for you and one for her, along with the soft caps and mounts, would be a great start (figure $150ish for the cap and shroud and $400ish for the mount, each). Really ought to at least try a soft cover given the price before buying a helmet, I swear it'll always be useful even if you do get a helmet. If not and you get a black one, I'll buy it off you.
You can always pair up the 14's if you get 'em with matching tubes later on if you wish (say she's not with you) or later on you decide on another set like those 15's.
You also probably need to invest in an IR light of some sort. Surefire V series lights light up a wide area close in really well but you'll need something more focused for longer range. Also need to consider IR lasers, maybe a PEQ. I have a Mepro Mor and it has a tri-power dot sight (battery, tritium, fiber optic) and it has a 5mW red laser and 5mW IR laser slaved to it, so zero one, zero 'em all. It's a bit tall so irons won't co-witness if that matters, it was originally designed for the Tavor (so if you have one of those it'd be the bees knees --the switch fits in the handguard and the cable routes inside the rifle I think). Works fine on AR's though and the 5mW IR laser is much better than the civilian power ones, especially in fog, etc. It's not TOO powerful, but still gotta treat it like it's 1000mW. Be safe.
If you get a 14 and want to weapon mount it, which would be cheaper early on and give you time to recover and save for lasers and such, PM me before you buy anything, I've got this low profile Larue QD mount and QD optics mount that goes with it and I'll let it go for a lot less than new. It basically is new, bought it for my wife who didn't use it and got a divorce so I don't need it. If you're gonna put it behind a red dot or EoTech it's the way to go, just get a sight with NV setting so you don't burn a spot in your tube.