If you've never attended a commercial embroidery trade show before, I highly recommend that you do. Trying out all the machines at one location and in one day will give you much more understanding and "feel" for the machines and how they stack up to one another as supposed trying out machines in different locations and at different dates. Not to mention the trade show discount and bonuses you'll receive if and when you decide to buy so put your haggling hat on 'cause prices aren't written on stone
If I were you, I would stick with the popular brands like Tajima, Barudan, etc. They cost more, but time and time again these machines continue to be the known workhorses of the industry. It's much easier to get support and parts as well as find qualified technicians. I'm not just talking about support from distributors, but support from other embroiderers as well--especially online. Resale value is another aspect to consider. Just like cars, you want a machine that can retain its value better. In short, they're a better investment.
With regards to choosing a single- or two-head machine. Recently, SWF introduced dual-function machines. In the case of a two-head, basically, it is now possible to embroider a different design on each head. I don't know how much you know about commercial embroidery machines, but with the exception of SWF, having a two-head does not mean you can do a different design on each head at the same time. So if that's what you were thinking to get more done, unfortunately it does not work that way.
I really don't think you'll need a two-head for the "personalized" gifts niche especially if you have a "small gift shop." You will receive plenty of orders, but most of the orders will be for personal use and therefore in small quantities. If you were targeting the corporate realm where company logos will make up the bulk of your orders and therefore "identical" designs will be embroidered on dozens and hundreds of items on a single order, then multiple heads make sense.
As far as features are concerned on modern single-heads, popular embroidery machines are jam-packed with features. These machines can pretty much meet your requirements and then some. Get as many needles/colors as you can afford. Having a 15-needle machine brings convenience and productivity to a new level. Since you're in the gifts market, you may want to consider getting a portable/compact machine if you take your business on the road at fairs, shows, and so on. These types of machines are fantastic! Moving them from place to place is a breeze.
Samantha is right; a commercial machine is world of difference compared to home machines. Give us an update on which machine you decide to buy