Hi, and the same to you.
I've never dealt with such a beast yet, but IMHO I would treat it just the same as you would buying a laptop, buy the best CPU you can afford, and check out the ram, needless to say get the most you can, BUT, don't put off buying a specific model just because it has less than another model, instead before deciding, check out if it can be upgraded in that model, and to how much, also note the amount of slots, that will set out what size sticks will\could be needed, because if the slots are limited, you may have to buy sticks where each single stick would have to be of a size that can make the cost an issue.
Don't worry too much about storage, external storage can be bought fairly cheaply these days, look at connectivity as well, USB3 is a must IMHO, but a point I will make is about the amount of USB devices that would be connected to this, and the amount of ports available, I don't know for sure, but to air on the side of caution (unless someone has a conclusive answer\insight) would be to use an externally powered hub, as I don't know how much power it's own ports can manage, but that's only if there are a lot of devices that could be used at the same time.
Not sure what else to suggest, apart from the obvious check out reviews of any specific model your looking to get, and make sure there are no "known" problems starting to come to light, or any other problems that seem to affect it's performance etc., otherwise I would just treat it like a laptop, and needless to say 64bit OS, but most are these days anyway, but it is easily overlooked when looking at so many different aspects of something, hope this helps a bit anyway.