Help needed refinishing

Hi all

A few months ago i asked a question regarding a hardwood table that i had bought that the surface was damaged, the finish was raised in splotchy areas, bit like water or heat damage.

Anyway, a friend who is a carpenter suggested sanding it back, which is what i did by hand using 360>600>800>1200 wet and dry paper. The finsh is silky smooth, just whhat i wanted, however it is still streaky, i cannot even with 1200 grit paper get the patchy sanding lines out especially when the light shines at certain angle (90 degree overhead its perfect, but glancing light shows it up). The center folding section of the table is undamaged and i left it, so its like new, even though not as smooth as the 1200 grit finish, it does not have 'streaks'
.I have then used a random orbital sander with 400 grit paper, which has removed the lines, but the surface is still 'grey' and ghosty, and standard polish will not make it perfect, and their are still some random sanding orbits, though less noticable than the ones done by hand.


So my questions are:

1. If I ever want to get back to a uniform smooth finish is their anything i can use over the top to smooth it all up, bearing in mind i dont have spray equipment. If so what type of product.

2. How do i prevent either brush strokes in the surface, or sanding lines if i sand back a finish ?

3. How does furniture bought at a showroom look so uniform and perfect, but even when i get a smoother and silkier finish it is still of worse appearance

4. Are greater than 400 grit papers available for orbital sanders.

the tableis a dark rich mahogany colour, and i believe it is some sort of polyurethane finish as the dust was white and no grain was lifted when sanded.

thanks in advance