changing website – novice here

Hi

A few months ago i’d not even heard of wordpress (i know…). Since then, i thought, this is the way to go – i liked that i could add content and adapt without paying a 3rd party. So i got a guy on Design Crowd to do a a site for me. https://www.thepropertyplan.co.uk.

Not the best i’ll admit. Its slow and clunky and since then i’ve learned about themes (ala Themeforest). One in particular i think would suit my business site very well – The7
https://the7.dream-demo.com/features/full-features-list/

These will look a lot sleeker and i am sure will be faster, plus they are much more customisable and adaptable.

I’d like to set this up in the background, then when its ready, take down the existing site and replace with the new one. I have literally no clue as to how to do this.

I’ve bought several plugins on Codecanyon which i’d like to use on the new site too.

Is it possible to set up a new site in the background? how do i go about this? can i use existing plugins i bought on the new site – or will i have to take down the new one completely?

Any help much appreciated.