There are few decisions that will doom a software development project as surely as picking the wrong people for it. The problem, of course, is that the people you actually need on the project are quite rare and getting hold of them for your project even if they're already working in your firm may be tricky - if their current project manager is even slightly awake they will really not want to let them go.
Joel Spolsky reckons that his key criteria for hiring is "smart and gets things done". With all due respect to him (after all, his firm has bashed out some commercially successful software over the years) I don't think that's enough. I would modify that to "smart and gets the right things done". I've known any number of smart and productive people over the years who spend at least half their time doing work that never ends up being used - either it's irrelevant to the main thrust of development, or it does the right thing but in a way that's never going to scale. Someone who's always asking themselves "what does my current work actually do for the project?" will be at least partly aligned with your goals.
Get people who are familiar with the technologies you plan on using in your project. The ideal is to find people with experience developing either at the size of code base / complexity you are aiming at, or at worst one level below that (so for an estimated 100KLoC Python codebase you should find people who have written systems with at least 10KLoC and preferably at least 50KLoC of Python). Never use your project as the basis for testing a new technology - or, if you must, confine it in one place in your design and have a fall-back plan if the new technology doesn't cut the mustard.
Good developers need an ego - they have to take pride in producing the best possible system - but they also need to be able to take criticism and deal with it appropriately. If your developer is a prima donna, you're going to end up with the system that they want to build, and damn the customer.
Always consider the one-under-a-bus rule. Your team should be able to tolerate any single team member being run over by a bus, minimising the inevitable resulting delay to the project. This means that no team member may be irreplaceable, and you should ensure that each system component (which as noted above is probably developed by a single team member) has at least two team members who are capable of developing and testing it. If you're requiring that any code change be reviewed by another team member, this should fall out automatically. If you see a team member actively hoarding information and expertise, you should seriously consider dropping that person from the team. I assure you that ignoring the issue and hoping for the best will not improve matters.
You need to get your team size right, and my personal feeling is that the team should be as small as possible but no smaller. The problems caused by oversized teams, or teams that have people firehosed on them late in development, are well documented. Fred Brooks Jr's "The Mythical Man Month" is timeless, and peerless on this subject. Start by picking out your developers; you need at least two (one needs to check the other's work) but no two developers should be focused on a single part of the system. Slice up the design between developers.
Once you know the size of your development team, consider what you want to do about testing / QA. My finger-in-the-air rule is that the testing / QA headcount shouldn't be more than half the developer headcount, and quite possibly less. Perhaps you need more of them in the first couple of months when you're building out the unit/system testing and developer environments, and fewer in the middle phase before customers get their hands on the system.
If you have anyone technical on your team who is happy doing repetitive tasks, you need to re-educate them. With a small development team you don't have the spare resource for someone to spend their day pushing buttons. They should be automating wherever they can - everyone should be happy in a scripting language like bash, Perl, Python or (heaven forfend) .NET.
Don't forget the support that won't be part of your official team but is nevertheless vital - sysadmins who maintain your hosts, admin staff who handle your procurement and organisation. Don't try to do their job yourselves. A talented developer who is spending half his day deploying new OS images is not making good use of your limited time.