Multi country seo

Hi Guys

Hoping you can help.

I have a uk landing page getting getting great sales in its niche.

I have decided to build out this site with content to try and get some organic traffic

At the same time I have decided to dip my toe in the us market.

My uk site is .co.uk

I will need a seperate page for us visitors for currency and other obvious reasons.

My question is should I focus the authority on the .com and make the uk a subdomain of this .

Or should I get all content rewritten and build two authority sites side by side and link each other .

Any advice most welcome

Please go easy im brand new