If you have a 6 foot fence, and in places, 3 feet of it will be covered up with dirt, then why don't you take down that section of the fence, put in your retaining wall (you'll need a two sided wall....which becomes an elevated planter) and put an attractive fence on top of it. Cement backer board might work for a little while, but what happens when the fence needs to be repaired/replaced? Also, think about what purpose the retaining wall serves. Sounds to me like the potential is there to have a brand new eyesore in your yard. Maybe I'm just not visualizing it properly...

It can probably be presumed that the lot grading for the subdivision is such that lots are all graded to drain independently out to the street on each individual property, so that creating a drainage problem for a neighbor is not likely, but then again, this lot could have slopes and drainage across lot lines, in which case interruption of flow is an issue. My understanding from another post by the OP on this same garden was that theot was flat, and the intent to build raised beds was more for aesthetics as well as making vegetable raised beds that would have improved soil conditions and be easier to work. The idea of a french drain as sketched out by the OP, which seemed to form a circle at the base of the proposed raised beds but didn't actually connect with anything, didn't seem to make much sense in terms of actually solving a drainage problem, in fact, if the lot is flat, they would seem to have been superfluous to solving the problem of a wet crawl space under the house, which sounds more like it was related to roof downspouts unconnected to drain lines to take it away from the house. I had originally understood the back of the lot to have the lot behind it at a higher grade with a slope beyond the proposed raised beds, but the sketches did not appear to support that line of supposition. In any case, I'd suggest that the OP either hire a competent landscape architect or designer/contractor to give him more informed advice on solving his problems and avoiding unnecessary expense or useless construction, or read up more to become better informed about landscape construction and particularly drainage concerns as they would pertain to his Fremont location. As it is, the questions have been too general to give truly informed advice, and not enough information has been supplied to really address all the potential concerns. I'd hope that these discussions have been sufficient to alert the OP that he needs to either hire some informed help, or get up to speed with the information needed to make the best decisions on how to proceed. There are definitely times when it saves money and expense to hire expertise...

The proper vent pipe to be used going through any combustible material, such as wood, must be a double wall B vent type. It's essentially a pipe within a pipe. An air space around the inner pipe keeps the outer pipe cooler and prevents any possible combustion with direct contact. There is no "sleeve" of any sort to go over what you have there now. Any reputable plumbing supply carries it.

I don't think you'll need it that high. Cars will be below the rise. And a dense shrub like a ninebark will pretty much block off the sightlines in winter (perhaps not headlights, if those bother you). That said, holly, rhodos, azaleas and mountain laurel will all do.