Well, here goes nothing... We've been in the house 20 years, with mostly a combination of fake hardwood laminate and horrendous builder-grade carpet. It's time for some upgrades. The fireplace went in first (mostly wood heat through the winter), and we're also replacing the kitchen cabinets. The plan is to put the hardwood in first, and the cabinets on top - yes, I know there's a great debate over that, but that's not what I want to discuss in this thread! I'm trying to attach a layout (maybe in the next post), and my plan is:

1. Start in the center of the house, above the main beam in the basement, and lay the wood in opposite directions.
2. Expansion gap of 3/8" around all edges. I've removed all baseboards and will replace with new, painted baseboards - at least 9/16" thick - I'd prefer not to use quarter round.

What else do I need to consider?

Not sure if I'm linking the image properly for this forum, but the plan is to start at the red line. Just looking for suggestions to make my job go better, as well ensuring there aren't any potential problems I may have overlooked. Thanks in advance!

Did you check the sub-floor for flatness? Is the fireplace slab going on top of the flooring?

The subfloor is as flat as it's gonna get - not terrible, but I'm aware of a few places I'll need to shim. It's obvious that when the house was built, it spent some time in the weather before it was completely under roof. With the current laminate floor, there are a few mushy spots where the subfloor sags slightly between and across 1 or 2 joists, most likely due to inconsistent joist size and sloppy workmanship when it was built. The joists sit on a steel beam, so no issues below.

The fireplace slab is already in place, and sits on a properly constructed non-combustible base, which elevates it 3/4" above the subfloor. I should be able to bring the planks right up to the slab for a clean finish with no trim pieces... at least that's the plan.

Thick tarpaper like 3 tab shingles make the best shim. It is about an eight inch thick and will not compress under normal conditions. If you use it like a contour map to build up the low spots that you find with a straight-edge the floor can become flat. Slide the paper under the straight-edge adding another thickness if necessary marking the boundaries of the different layers as you go right onto the floor. Then cut the layers and staple them so they don't move before you cover with Kraft paper.

I'm familiar with that technique to build up low spots and have used a variety of materials on some laminate flooring installations, including roofing felt and sheet linoleum. I've heard about using shingles, but I'm always afraid the stone-like material could come loose and sound "crunchy" after many years.

What would be the purpose of "Kraft" paper? Isn't that just thick paper? I've often heard of rolling out roofing felt. What's really needed and what purpose is being served?

Waterproof Kraft paper is strong. It will help the low spots have a bridge so any ends of planks will have a little support as they get laid keeping the plank in line until the next board gets put up against the row.. Since the thick tar paper will be an eighth inch above the adjacent area ( wood flooring needs to be within an eighth in six feet to be considered flat) the new row will slide against the one already laid much easier. It helps to have the gravel side down. Having waterproof Kraft paper helps to keep moisture under the flooring from contacting the flooring. Some moisture will move through penetrations made by the fasteners but this moisture usually evaporates through the surface of the finished wood so cupping from moisture below the flooring is diminished. On the last rows of flooring where there is tarpaper build up near the wall, latex sub-floor adhesive will hold the tarpaper in place so the final row can be held more securely with fewer top-nails.
Roofing felt is another option. The main disadvantage for me is getting it in place without touching the painted walls. Hardwood flooring is the last trade to finish in the home, just ahead of the wallpaper. Careful installation will not have a callback for the painter. Sometimes the mechanic will like to have the flooring slide together easier. Tarpaper can be stickier than the smooth Kraft paper so the flooring will not slide together as easily when driven by the installation method.
Linoleum is a perfect shim, too. The three-tab shingles are flat to begin with.

Just ordered all the wood and ended up expanding the project by 50% (see layout here https://freeimage.host/i/whole-floor.2ghLVR). I'm now planning to do the entire first floor, with the exception of the bath and laundry rooms. Red lines indicate where I'll use splines to reverse direction. A couple questions:

1. From the center line above the dining room, can I run all the way through the dining room and sunroom without any expansion joints? Its 31' from the top of the staircase to the back wall of the sunroom. Any concerns with expansion over that distance?
2. As I work from my starting point at the staircase towards the front door, how do I ensure everything lines up when my boards converge on the end of the staircase closest to the front door? Is this something to worry about, or will I just be ok as long as I install all boards tightly.

If you fasten the floor down vs. float-in you will not need to worry about the width of the floor if the wood has been acclimated. If the flooring expands or contracts you may get cupping or little gaps between the boards, but not much change at the walls. If the floor gets flooded the cumulative expansion will pop the nails free as the boards move toward the wall so the pressure that the expansion makes will not push the plate and damage the framing.
Constant even pressure will make it perfect. A little variance will not make much difference across the short distance at the end of the stairs "opening".