I am one of those who has never, ever sold a gun. I expect I will die with every gun I've ever bought, except those I give to my kids along the way.
That said, there are things worth selling for. I think you have to look at it in two steps. First you have to decide what's more important to you. Is a house more important than a gun? How much important?
Then you have to decide if selling the less important thing will really help you get the more important thing.
House: For the first step, I don't know how important a house is to you. It is typically a very good investment. It is also typically very expensive. My downpayment on my first house was 25K, and I was probably in a cheaper area than you are. Plan on 10% of the value.
Also, you have to plan on living there for awhile, even if you get married. Buy a dump and she will want to sell. Transaction costs of moving houses eat up any profit real quickly. If you do plan on getting married, it may be better to wait and let your wife help you look. DON'T let your girlfriend help, IMHO. Too much pressure on the relationship.
Anyway, I've seen a number of guys buy houses, get married, and watch their wife gut and refurbish the house's interior to make it "habitable." Unless you have far better taste than I, not to many women will have your taste in interior decorating. In your shoes I might suggest waiting to buy a house, even though normally I think its a good idea to do it.
Second, you indicated you have about 2K in guns you could sell. Not much of a dent in a house buying process. Personally, I don't think the small gain you make towards your downpayment is worth the hassle and transaction costs present in selling your guns. Not unless they are guns you don't want anyway.
Engagement Ring: First part: you have to look at this through the lens of your faith. I doubt many posters, if any, responding on the thread is looking at it like your faith says you should. Some of the guys here don't place much value in marriage, which is their right of course, but it strikes me as very different than what you see as valuable. I'm not Jewish, but my faith views marriage in a somewhat similar fashion to what an Orthodox Jew would, so I tend to think the ring is more important than the guns. I would sell my guns if that was important to my wife. My marriage takes precedence over everything else, my things, my job, etc. Only my faith comes before my wife.
Second part: unlike the house, 2K from guns will go along way for a ring. Shop smart, check the internet for rocks and bid your jeweler down based on what you know to be the true cost of the rock, and you can do quite well. I still hesitate to sell to buy a ring, but that's just me. If you don't care much about the gun, hey, get rid of it. Put the money away for when you want to use it, whether it be a ring or whether it be a new gun later.
CAR: Hey, buy the ring first, and wait a couple months to see how the relationship is going. Don't buy it all at once. That said, I can't see selling for a car given that a car isn't all that more important than a gun, so long as you have one that works.
On the other hand 2K is a good start for a good used car.
So, my summary: House, no. Ring, yes. Car, no.
Good luck,
patent