You are on the right track - first you need a cedar cleaner sprayed on with a portable hand pesticide and weed killer type sprayer for designated soak time, then power-washed off VERY carefully, always with the grain not across, and never with a jet nozzle - use a diffusion/fan nozzle and keep far enough back so you do not gouge the wood or raise the grain, and never directed upward, because it will get under the boards and wet the substrate. Experiment first on a scrap board, then start on the least visible part of the house, so you have your technique down perfect by the time you get to the visible faces. Properly done, the pressure washing is done board-by-board, always from the "up-grain" side - meaning toward the way the surface grain is tapering out on the surface, not "against" the grain, which will lift the grain and make it fuzzy.
I would recommend using the cleaner made by the company as the stain, so you are sure they are chemically compatible - some cleaners have chemicals like phosphates or boric acid that, even after washing off, can cause blistering and bubbling of some finishes applied over them.
Then, after drying, you need to apply a mildewcide, though some stains come with it in them, and others can have powdered mildewcide added to the can before mixing.
You will never totally get rid of the blotching and uneven coloration without deep sanding or removing the boards and re-planing them, which is just too expensive for most homeowners. Also, assuming it was previously stained, some areas will absorb more than others. Therefore, using a darkish stain is your best bet, rather than clear. I would EMPHATICALLY recommend a penetrating oil stain rather than varnish, urethane, or water based stain. The latter tend to turn orange and peel off after very few years, and do not penetrate the wood as well when applied. I would also recommend a non-building stain (not a heavy bodied (lots of solids in it) or gloss-finish curing one), as the stains with heavy body and build tend to peel like paint after very few years, and quickly develop dull and shiny contracting areas. Make sure the product, if a stain rather than a penetrating oil, has a Ultraviolet (UV) inhibitor to reduce sun cracking, fading and blistering.
While log oil type products can work, I would recommend against them for general use for 5 reasons - they stink for weeks to months afterward, cannot be recoated in the future with anything but the same products, stay tacky or sticky locally for months or years, usually makes the wood REALLY dark, and really makes the exterior fire susceptible as the log oil is highly combustible for a decade or so. However, it does have the advantage of being more waterprooof by nature than most stains, generally lasts longer, and is easily recoated, so log oil or linseed oil based penetrating oils are commonly used in camp cabins and vacation cabins out in the woods. Linseed oil products may attract insects like ants, earwigs and beetles, so you make create a problem that way - petroleum or turpentine based oil products do not.
The wood needs to be TOTALLY DRY before staining, which can be tough in some parts of the country - you may have to tarp a side at a time from the eaves (leave adequate airflow by the wall for evaporation) to get enough drying days (typically 3-5 consecutive days without rain or fog), otherwise you will get more blotching, and areas that peel. You also need to be prepared to tarp it or be absolutely there is no chance of showers for at least 24 hours after staining, as water on the fresh stain makes it blotchy and will result in wide variations in surface appearance, as well as bubbling the finish.
Plan on doing two stain coats a couple of days apart, and spraying works MUCH better than roller or brush, just because it does not miss any spots because of the roughness of the wood. Even though sprayed, plan on doing manual brush-out finishing, because you will get runs in areas where the previous finish was relatively intact or the board was smooth rather than rough.
I have not run into Penofin - I like Olympic cleaners and stains myself, but I have a couple of neighbors who got very good results using the Behr line in the past couple of years.
I would also read a few of the articles and blogs on the subject, particularly those by the cedar wood associations, by googling this search phrase - cedar stains