I'm sure truing can be done without a stand, but it's a whole lot easier if you have one.

Since it sounds like you don't have a good go-by wheel to match wheel tension, or a half-dozen years of professional wheel building experience, I'd suggest adding a tensiometer to your wheel truing kit -- possibly even before a stand. Once you've got the tension up where it needs to be (about 105-110 kgf), stress-relieve all the spokes, re-true if needed, and the wheels should last a long time without needing any work. As a clyde and an amateur wheel builder/repairman, I've learned a lot about how poorly tensioned wheels go out of true and tension. Getting the tension right prevents a whole lot of problems with nipples unscrewing, spokes loosening, and even spokes breaking.