I just made my first HGVC purchase, and made some of the same calculations that you're making.
If you're torn between 5,000 points and 7,000 points, but you think that 5K might work for you, you'd be much better off looking for a 4800 point package, somewhere, than a 5,000 point package. Your annual membership fee will be much higher for a 2BR Gold, than for a 1BR Platinum week, and your cost to buy in won't necessarily be that much higher. Between 5000 points (2BR Gold) and 7000 points (2BR Platinum), the membership fee will be identical at the same property, and you're getting 2000 fewer points.
I got a 4800 point package (1BR Platinum at Sea World) on eBay for $2500, and it passed First Refusal. I was a little nervous about having my first ever purchase be on eBay, but the price was lower than any listing I saw from a real estate agent for similar packages. Before making my offer, I came here, and did a search on the name of the company running the auction, their eBay user name of the seller, as well as the closing company they use. There were positive comments about all of them from other Tuggers, so I felt pretty secure placing that bid. The transfer isn't complete, yet, but so far, everything has gone smoothly, and I've had very good communication from the seller, and from the closing company.
As far as membership fees, for 4800 point packages, the three lowest properties for 2015 were the Boulevard/Strip location, the Vegas Paradise/Karen location, and Sea World. For 7000 point packages, the lowest membership fees are Boulevard/Strip, then Paradise/Karen, and then Flamingo. Some of the other Orlando properties have membership fees that are lower than your budget, too, but since points are points, I'd aim for the lowest membership fee that you can get at the best buy-in price.