Hi all,
Here is my situation. I really need to insulate my house. It is a 1929 tudor with half the attic open (other half two finished bedrooms though a lot of it, we think, accessible via the ridge). A couple of walls (kitchen, bathrooms) have spray foams insulation from a renovation 5 years ago, though most walls do not.

I’ve been obtaining dense pack cellulose quotes and various open/closed spray foam quotes. I find myself lately shying away from foam quotes (though not enitrely sure why).

Other details:
1. Unvented attic
2. No vented soffits
3. My roof is shingles (normal…) over plywood. Frankly I don’t know if there is a layer in between the shingles and the plywood. If this is necessary I will find the answer.

Pointed questions:
1. Do I need a vapor barrier or retarder in my climate (Westchester County, NY). I think we are a 4.
2. I have been mentally toying with foam board with closed cell from a can to air seal at sides for those areas that are open and accesible. Then rockwool over it. Please provide your critique and what you think is best from a cost/value perspective. Also what I can do with a small crew from a DIY perspective.
3, For my rim joist, most of which is very accessible, what do you think is better. XPS with closed cell foam to air seal or rockwool with closed cell foam to air seal?

Thank you for all your help in advance! Feel free to send a link or article if most of this is covered.
David