I suggest starting with the 5%.
It takes about 3-4 months to even see any changes in your hair, as it takes that long for a hair to go from the initial point of growth at the follicle to a sufficient length to be seen emerging from the surface of the scalp.
Takes even longer than that before any determination of effectiveness can be made, and the general rule of thumb has been to wait a year before making any judgements about cosmetic impact.
It's been great for me. Regrowth has been modest, but in a cosmetically significant area (the upper corners of my bald temples). Then again, I'm an older guy and I've been bald in this area probably a lot longer than you folks. I wish I started it earlier. The most cosmetically significant impact that minoxidil has had for me is in a dramatic improvement in my hair that was existing, but thinning. The thinning has been reversed and the thickness is pretty much back on par with the non-affected hair in the back of my head.