Your on the right track, you want the water to run away from the seams. Try not to nail on the top of the flashing to leave nails exposed also, folks do this all the time and caulk over the nail...this leads to leaks later on. Instead have a sider prebend your metal flashing if possible. I use metal roofing products for sealing the joints also. You can use a good silicone and overlap the pieces by 4 inches at the ends.
When you install the flashing it needs to go under the building paper at the wall, not just under the siding. If you use copper, make sure you use copper nails, otheres will corrode...accept for high grade stainless of course.
Just keep it simple, be the water and you should have no leaks.