My PR is just to front of middle (marriage wall) of modular home, on 1st floor. Why does the vent stack for it come up close to front (in kneewall area) in attic? The main stack is in the back of the house (where kitchen and 2nd floor baths are), they left a space b/t joists in attic with no flooring (just plywood) so plumber could connect onsite, but he didn't want to put a large hole/notch in center beam of attic floor (running north/south, joists run E-W) so he put a Studor valve. It smells when it rains. Should I have someone bring that single stack up through the roof (it'll end up being just to one side of center gable unless we can do a horizontal run to the south, but I don't have much height in kneewall area of attic)? Maybe it won't be too bad looking if we put a "dryer vent" type cover on it instead of leaving white pipe sticking up like they did in back?

We did the same - cooktop side 36” and sink run 38”. we do have 55” aisle between them but you would really have to be looking to notice that they are at different heights.

Agree with all the above on Manual J and S and addressing all this in the design stage. Ensure they're not fudging numbers or using "rules of thumb" (if it works out to 500sqft/ton or thereabouts, they likely didn't do the calculation). We had load calcs done on our house by 3 contractors. One came up with 6.5 tons, the other 2.5 tons, the third 4 tons. The 6.5 tons one was clearly just fudged/used a rule of thumb. Our builder would have gone with it had I not asked/researched the types of questions you're asking, so good on you! A few things that came up in our build I wished I'd known earlier -- ask to lay out the supply/return registers ahead of time so you can plan around furniture and such, and also the size of the returns -- if you want 4" thick filters, make sure they know and plan for that, and also make sure that the size of the returns match commonly available filters vs having to special order them. Return size can affect noise as well, if too small. Also on returns - good to understand if they'll do dedicated returns in each bedrooms, transfer grilles, or jumper ducts. Make sure the system will stay balanced when the door is closed.

I can't say for sure, of course, but I doubt there's a coating on any oven equipped with pyrolytic/high-heat self-clean that can survive 930°F but not exposure to chemical oven cleaners. My supposition is that an advisory against chemicals on those models is related to the concern of noxious fumes from exposure of residual cleaner chemicals during subsequent self-clean cycles. However, models equipped with only steam-clean may have a coating of some ilk to help avoid soils adhering to the surface that could be damaged by chemicals. I have seen a few models that have both steam-assist cleaning and regular high-heat self-clean, user choice which to run at any given cleaning operation.