Just use common sense here. Look at the condition of the subfloor boards. What are they made of and are they still mostly stiff and flat? If they haven't sagged between the joists in 80 years or so, they're not going to do that now. Although the book says install finish flooring perpendicular to the joists, I would not worry much about that, especially where the subfloor material condition is as I described. Simply make sure that the subfloor is well-attached and sqeak-free.

Oops, sorry - I should have mentioned that we have a slab foundation. Here's the link: www.truehardwoods.com If you call and talk to Justin (it's a family-owned and run business), tell him hello from the customer that bought 70 cartons of Castle Rock Birch shipped to Texas! We're installing it ourselves, so we decided to do floating. He recommended we use the Silencer underlayment.

That makes the flooring look more real but honestly you can do either since you need a sub floor before installing them

ok, you sure you want to use laminate? you don't want replace the 2.5" (or 3.5'?) oak flooring? if you get the unfinished T&G stained on site, you may be able to salvage some of the flooring. (even though it may looked thrashed, you'd be surprised at what taking off a layer and re-staining them can do. I've refinished wood that looked like it belonged in the garbage. when I redid it, you'd have sworn it was new). Have you called out a reputable company to see what they say? The reason I'm pushing it is, hardwood or engineered is always preferable. LVP is not long lasting and certainly isn't a trade 'up'. Flooring is one of the most important upgrades in a home, so you shouldn't scrimp. remember, wood floors will be the last flooring this home needs for 50 years (barring disasters). vinyl lasts, what, 10 years? if you had to replace it 3 times, would it still be worth the lower cost? You think those gray vinyl planks will still be 'in' 8 years from now? I can tell you w/100% that the wood will still be in style. And the stained wood will look so good next to your black brick. Kudos to you for picking a bold choice. what else do you plan on doing in that room? what color were you going to paint that fireplace wall? doing any wood furniture? rugs?