Unfortunately you guys missed one of the best VGF sales that ended last week, the current incentives don't end until near the end of October so don't rush it like
@aceshigh73 said.
In general I don't recommend buying in anything with someone you're not married yet but also I'm a hypocrite and bought
DVC with my now fiancee about a week before we got engaged. It seems like you two already own a house together so at this point a separation would already be sticky but anyways onto your main questions.
1. I would buy the amount that YOU and your partner need. Don't take into account family or friends needing to stay. For one, people are unreliable and cancel last minute. If they really plan to join you that often, they'll consider buying their own contract. For the times when you want to do a big group trip, you can always skip one year and bank for that trip. If you find yourself borrowing way more than you should be, you can always add on down the road. Having that occasional skip year might be good for your BF who doesn't seem like he's as big of a Disney fan
2. This has already been answered but avoid using Interval or using your points really for anything other than a DVC stay including Disney Cruises or Adventures by Disney. You're better off renting the points and paying cash if you decide to use them for anything but a DVC stay.
3. As has already been answered, the good thing about DVC is the number of points in a resort cannot change. They can't magically add points to the resort and dilute the value of your points. They're allowed to change the cost of a room during different seasons but if they increase the cost somewhere, they must reduce the cost of another room. Equal exchange. This is why the older resorts are so dirt cheap. Resorts like Old Key West have
point charts that were made in the 90s.