Website design and another question

Related to this thread https://www.blackhatworld.com/posts/11664891/

In the next month i will start to work behind the project described in that other thread of mine (tldr, a website related to a big instagram account of mine).
I decided to do everything with a certain quality and so i thought to buy a website design on 99designs, a thing that i never did before and therefore i know almost nothing about.
How does it work exactly? Do i have to tell the designer like if i need it for Wordpress or other platforms and then after the work is completed i just upload the theme? Or is there some kind of backend someone have to do?
Basically the website will be (in the beginning at least) a normal news website with a store, but obviosuly the theme will be very personalized.

The other question isn't actually a major thing: i bought a .to domain for the website, because i found it with the exact same name of the instagram account (which is a pretty common word, therefore very hard to find a clean domain with it). Do you guys think it'll be ok? It's like doctor.to, architect.to or stuff like that, to give you an hint

looking for advices

I would go for a .com domain, these type of domains you've listed have very little credibility yet in my opinion.

If your net goal is to send traffic directly from Instagram, I'd think .to is probably alright. People that click through from your profile won't be too precious about the TLD, in my opinion. If you're looking to market via SEO etc. over the fuller course of time, I'd recommend sticking to more common extensions. It's easier to remember and is more orthodox - and therefore more trustworthy - for visitors. Maybe start with .to and - if you do need to expand channels at a later date - look at acquiring a new domain in due course, once it's earning decent revenue already.

99designs is over priced, post on freelancing sites for a better deal. In the meantime do research on what is needed so you can portray your ideas to the developer accurately.

I don't think this type of domain names would get you much credibility on a first impression.