The most important thing is usually your portfolio of visual work. A close second is your recommendations. If you have professional experience in architecture then you may (or may not) have some work worthy of inclusion in your portfolio, and you probably have one or more professional references. In that sense your work experience may be very helpful to you. However, it is not critical that one have any professional experience whatsoever to apply to a first-professional M.Arch program, and having such experience is not an automatic edge. For example, CAD drawings of run-of-the-mill projects on which you had a limited or no design role are unlikely to be looked on favorably, but examples of an innovative and/or fabulously detailed element/construction/part of an architecture project on which you were a lead designer may be much more influential in your portfolio.
What sort of "side courses" are you interested in taking? Anything that will add to your portfolio will usually be helpful. Any type of freehand drawing, graphic design, color theory, theory of representation, etc. will usually be helpful both in your applications and in your early work in your M.Arch program.
It is difficult to choose one scenario over the other without knowing the specifics of what you are considering.

I got my bach in visual arts, it's all here:

http://www.archinect.com/forum/threads.php?id=20590_0_42_150_C

also, at the University of Florida Core M. Arch program (for non-architecture undergrads) looks at the Letter of Intent quite heavily, because this will illustrate your interests and thought process.

most places 3-year is misleading. it's three and a half, which many stretch out to 4 (who wants to graduate in december and take all 15 hour courseloads?) here's to 8 years of college for a master's... (9 for me, hooray!)

portfolio of anything you've drawn, built, crafted, painted, figured out, i think is most important. and good references.
good luck!