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Been a while since I posted anything on my journey in the world of finishing.
Here is what I have learned.
PREP
if your not going to take the time to prep don't finish

sand and level sides lacquer don't go past 220 grit. Use a block to get the surface as flat as you can. I then wipe off with Naphtha and mineral spirits at this time look CLOSE for swirl marks. I do a final sanding 220 with the grain on the back and side and across the grain on the top YES ACROSS THE GRAIN

Sealer
Vinyl but my preference is 1lb cut shellac. 2 coats brushed on with a GOOD BRUSH you may also use a rag.

My filler of choice is aqua coat but any filler you can use that works for you.

AQUA COAT I apply with a gloved hand and squeegee off , I have a 5 inch squeegee from amazon that works very well. Allow 1 hr scuff sand with 320 and apply another coat. Same method
allow an hr and scuff sand with 400 , look close and if your filled 1 coat of 1lb cut shellac

this I let over night so I can get a good look see on the surface.

My finish mix is as follow if your above 65 degrees and between 40 55% RH. I place 3 pieces of tape where the fret board extension is to measure thickness of my coat build

IN 1 QT NITRO 1 OZ RETARDER 4 TO 6 OZ THINNER
put this in a qt glass container and place in hot water get above 90 degrees
adjust spray gun , and I also heat my product to spray using a heat lamp or a hair dryer body temp is fine
this heat allows the viscosity lower and I don't need as much thinner,
Spray 1 coat allow 2 hr for voc to flash off do 3 coats
ALLOW TO REST 10 days
I will use an orbital sander and light sand the surface with 600 , 800 1000 grit to get flat DROP FILL any voids at this time now apply 2 coats using the mix above Last coat add a dash of thinner for the final coat
let dry 12 to 14 days
I use ASSILEX sanding system and NO POWER SANDER all straight line sanding. My buffing is to use the wheels first with Mazzerna finish , med and 175 then I use a dual action hand buffer and 3M finese it and maquires swirl remover also buffing and polish compounds from Mother , 3M hand glaze is my final polish set on 3 on my hand buffer
THE PURPOSE OF THIS IS TO GET THE UNDERCOAT AS FLAT AS POSSIBLE ,

Process is pretty involved, but the results are spectacular.

Nice work.

How did you learn/discover/validate sanding cross-grain on the top?

that is how a lot of good builders do it. That helps flatten the top with the grain can pull out the soft wood and make it dipped since the soft wood is less resistant to the abrasive.

John's cross-grain advice saved my tops. I was getting those little dips between the dark grain lines like he explains until I started using a sanding block and going cross grain. Those final tiny scratches can be a real pain in the rear to chase down for me on some tops. You think you are good but then when you seal it you see the tiny dark lines or dots here and there. grrr. I found this especially true with the Carpathian tops I tried. They sounded great when completed but I found them a lot more difficult to work with to get a spotless, clean surface to seal.

one thing I didn't note
finding swirl marks in the wood after staining can be frustrating. I just finished working on a Martin Authentic and I see them in there.

I would like it anyone would try this and get back to me as I am starting to do it

A on back and sides
when using a Random Orbit sander keep sanding to 1500 grit

I know I sand not to sand past 220 but this is whay

the finer grit leaves lighter swirl marks

now hand sand straight line with the grain with 180 on everything but Mahogany here use 220

spruce 220 across the grain after ROS don't do the higher grits
use a firm sanding block

That helps flatten the top with the grain can pull out the soft wood and make it dipped since the soft wood is less resistant to the abrasive.

That makes sense. Thanks for the response.