I have an incomplete site & host supports WP can I upload a custom WP site

Hi WP World,

I am a beginner & am looking for advice to help me get started on WP custom site building.

At the present, I have an incomplete site & host supports WP which is already to go, not sure how to use it due to the fact that my hosting company will not give me instructions or answer any questions re: building a WP custom site, with permalink buttons that link to database, sending client an email confirmation, also implementing drop down menus on custom apparel tab that will show designs line titles, then link from drop down to shopping cart to the specific line of their choice.

My question is can I upload a custom WP site w/out interrupting the site that is live? Can I build a custom WP website then load onto hosting server once it is complete? Can I create a database with 2 specific columns that separate people who join the positive movement & people who just order custom designs? and if they choose both then is it possible send only 1 email not 2.

Does WP support e-commerce? I am lost & do not know where to start.

Should I create my own site then load it or go through my FTP manager via host?