cart in front of the horse, but...
@Dana
size the boiler for the "after" picture of what it comes to post-insulation & air sealing upgrades, and be aggressive- don't use a 0F design temp or a 78F indoor temp "just to be sure"
I will admit that I did use the "just to be sure" (I was calling it 'err on the side of caution) method when I was building the Wrightsoft model, so that also may have kicked the heat loss up a bit.
Great ideas on all fronts for improving the enclosure, most of which have already been put into my longer-term budget. Unfortunately, and I know I am going to get beat up a bit on this forum, I am going to install the boiler before the improvements to the shell. We're a young couple and our budget isn't very forgiving, so I'm going to have to improve the enclosure over a longer period of time. Winter is coming, and I'd really like to NOT have to have another oil delivery.
After attending Joe Lstiburek's Building Science Summer Camp in MA this and last August, I decided that I am going the route of quality storms instead of replacements. It just makes more financial sense for us (see above). All of the windows in the home, save for a set of double-hung, fixed, double-hung facing east, are original Andersen sliders. The DH-F-DH will eventually be replaced, but I do like the design and character of the sliders, so they'll all probably remain, with the addition of storms...eventually.
Regarding the basement, I will have to review my model tomorrow for it's breakdown at the basement. The elephant
in the room
is the room itself, and the assembly(ies) you're recommending are something we've been showing at almost all of our retrofits; while I would love to do the flash & fill, I'll most likely be using the board + batt method. Because of dampness issues on the foundation wall (yea, by this point, you've gathered I bought a bit of a fixer-upper) I thought that XPS would be a better option. The 1" below the stud plate is very interesting and something I will now be adding to my drawings--1" is a hell of a lot better than a roll of sill sealer. The garage, with it's 12'+ of ceiling height should probably get the same treatment, especially considering it's directly below the bedrooms.
A point I failed to mention is the relocation of these mechanics, from one end of the basement. The current, original boiler is tied into the masonry chimney, but it creates an uncomfortable floor plan, so the desire is to move the new boiler to a more logistically (at least for future use of the basement) reasonable location on the other side of the basement. The relocation all but forces me to vent with PVC, 1) because of it's lack of a chimney, 2) because I don't have the space to run a chase chimney for a b-vent. Thus, I am a bit limited to what boiler I can install. Other than a mod/con, I have only found the WM GV+ series that allows for PVC venting. I have not dismissed the idea of the GV+, although, after @Dana's suggestion, I will most certainly be going with a GV+ 3 instead of the 4.
I am willing to "overwork" a smaller (undersized for current conditions) mod/con (or the GV) for one winter, while I go about improving the enclosure/reduce the heat load, than have an oversized boiler for the future 20+ years. Anything is better than the original American Standard oil-sucking beast I have now which can't be operating at much more than 60%.
While I don't know if I could ever get the home down to 25-30K (come onnnnnn MegaMillions), what are the thoughts about installing @
Dana's recommended "smaller" boiler to satisfy future considerations, although it may be taxed this winter.