I bought my first NV in Apr 2013 and have spent an avg 10 hrs per week outside since.
I had a $20k budget at that point and thought that would be enough for a one time "splurge" and I'd never need anything else (oh boy - was I wong !
)
I now realize getting into learning about and owning and gaining experience with NV/Thermal is a never ending process - NOT an event. So that's probably the most important thing I've learned over the past 11 years.
So consider "buy a little - learn a lot - buy a little more - learn a lot more ... and repeat until in the ground" vs a $15k type event.
Dual Tube NV is lighter than 2 x 14s but not as flexible. Its harder to have NV and longer distance Thermal spotter on your head side by side with DTNV. So this is a consideration. That said, 90% at least of other pundits, will say it is "insane" to put thermal on your head and it should only be carried in your pocket. Back in 2016 when the Patrol and Q-14 first came out and I posted about getting them to put on my head - I was told (literally) that I would get dizzy, fall over and die. Which miraculously (apparently) did not happen. But don't expect to be popular if you put thermal on your head !
On the other hand, being able to see critters (regardless of ilk) passively even in woods or moonshadows, handsfree while moving, is very liberating ... and if its on your head, you'll see that threat or critter faster than you would if its in your pocket. NV often cannot see critters when its really dark (overcast & no moon), thermal (almost) always can. For hunting/critter control, we really don't even need NV. For homestead defense, we must have both.
So thermal on head is a key decision BUTT not one you must make on day one. Though if you follow through with the idea of one massive purchase for a night gear, then you would have to make it soon.
As to Ballistic vs bump helmets. I have 2 of each and also 2 Crye Night caps and even 2 skull crushers. In hindsight, I think the extra cost and weight of the ballistics are not worth it. If you will be in 100+ gun fights or get shelled numerous times by mortars or fired at by RPGs dozens of times, then maybe. But even for homestead defense, it might not be persistent, never ending attacks with heavy infantry weapons. So, if I was only getting one helmet I'd get a bump. The primary purpose is as a platform to mount your head mounted NODs and bumps work fine for that. Making sure it fits you is critical (so avoid used - unless you love to tinker) ... upgrading the pads can help with fit and comfort, but most important - getting flexible counterweight system (like EOG) is most critical as you must balance the counterweight against the front end weight, which might be a lb or 2 !
Will you shoot with laser ? In the terrain you describe I would think its likely, so I would invest in a good laser setup and train continuously with it. Newer, lower cost VSCEL lasers are coming out that rival the military FP lasers (like the steiner dbal a2). New Holosun IRIS is something to watch out for. I would totally avoid low power civ laser units - the aiming lasers are usable, but the illuminators are useless. Its also possible to get separate aiming laser and ir illumn but once you combine with white light on the gun also, that gives you 3 items to switch and 3 switches is too many. Hence the combo ir/ir illum are indicated for one switch and the white light for the other. Being able to instantly switch on either ir and or ir/lum or white light is a detailed but essential consideration. He who fires effectively first wins the first engagement.
It might take a while to get this perfect, so don't be in too much of a hurry here. Let experience be your guide.
==
So those are key considerations to mull over !!
If I was starting now - knowing what I know. I echo evo9 and I would get a voodoo-S ... its really the first and only (serious) thermal that is effective at both the head mountable thermal role AND the clipon role, especially the clipon role. Expect to be able to engage minute of man sized targets out to 500-ish (if you can hit such in the day time). That would chew up about $15k of your $15k budget, but you'd know you'd be totally solid in this space. Then something like an Ops Core or Team Hillary (aka Team Wendy) bump helmet and a mount and a bridge - all that would run another $1k for serious gear.
Then a PVS-14. I have 4xPVS-14 all green tube and I paid an avg of about $2,500 for them over the last 11 years ... but green tubes are pretty much done now. The white tubers run from $3k up to I've even seen $8k for the extra/ultra high spec tubes. Another thing about me ... I am NOT in the "My FOM is higher than your FOM" club. For me any gen3 tube is good enough if it works and is not occluded with spots.
With one 14 you'll be able to put that on your bridge either with or without the VoodooS and be able to see the laser and have other observation capabilities that the thermal doesn't have (like see long distance vis or ir lights - i.e. detection of possible hostile presence). We need NV for homestead defense ( and you'll want to get a slip on/screw on 3x magnifier for your 14 one day to extend you observation range).
And to see lasers !
Then it would make sense to get your ir laser/ir illum unit vscel if possible and a separate white light. And get those mounted on your forearm in a very ergonomic arrangement that is 5000% auto repeatable for you to operate them and get the result you want each and every time.
IR laser/Illum and white light might run $1000 or a little more.
So with the lasers and the thermal clipon (in step 01 above) you'd have 2 aiming systems, the lasers for short distance, instantaneous engagements and the thermal clipon for further out.
Then a COTI ? Mounting a COTI on the 14 gives you a thermal overlay for shooting with the laser so the critter is seen by the COTI and the laser by the 14 and they are aligned so you can shoot the critter with the laser while you might not even be able to see the critter with the 14 (due to vegetation or otherwise). Shooting with laser, 14 and COTI is very fast, you don't even have to pull up, just aim and fire. Can be ~sub second with practice. I've killed about 25% of the critters I've killed with the laser. And critter controlling around the cattle and chickens in and around the woods is good practice.
And of course, shoot a little every day and night to keep your fundamentals honed. My goal is avg 7 rds per day, I am currently avging 3 per day for this year, but I know I must improve. Fundamentals are a fine motor skill which must be practiced all the time to be maintained. One per day is acceptable, provided its every day !
Good luck on your journey and welcome to the NV/Thermal world !!!