Saw your pics -
When weather permits, I'd recommend:
1) Treat the siding with Jomax and bleach, as per Jomax directions. A gal lon of Jomax should be enough to clean your whole house, as well, if need b e. If you're up to the task, scrub the siding, also.1.a.) After the cleaning is done, you might spray all the siding with strai ght bleach. If there is any deep mold or mildew on the siding, you might w ant to treat it with concentrated bleach, without rising it off. Do the s praying on a good dry day, so that the bleach better penetrates into the cr evices. Any mold or mildew (spores) may be deeper, than just on the wood's surface.
2) Seems you may have to trim the bottoms, up, at least 10". Use a sharp t ool or screw driver to stab the siding, to see where it is weak, rotted, de cayed, etc. Don't be afraid to stab hard. Draw your trim line above the d amage.3) Attach a board below the trim/cut line, so that your circular saw rests on the board, blade even with the cut line and beveled about 30 degrees.
4) Prime the cut, well, when you prime the rest of the siding. Once primed , mark the siding (where you made the cut) as to where your wall's studs ar e (re: #6 below).5) For your application, wooden drip edges, as I have, may not be the best application. For a different application, I bought some 10' angled flashin g, 4" on each leg, from Lowes.... like this
6) Once the drip edge is installed, attach the bottom edge of the upper sid ing to the studs, if need be. That bottom edge might need attaching right near the cut line, if the next higher attachment is too high.
7) Cut and prime for your replacement lower siding. Cut both top and botto m edges at 30 degrees. Prime the back side, also.8) Put a flashing along the lower edge of the building, before installing t he replacement siding.
The worst part of that job will be cutting the bad siding off. Kneeling an d cutting with a circular saw, that way, is not fun.... at least for us old folks.
Sonny