WordPress definitely would be my choice. And, in regards to monetization, forget about it. You need to focus on building topical relevance and authority in your niche and, your wife just happened to select a very competitive one.
Wait until the site gets some organic traffic before throwing any affiliate links or ads there.
Secondly, I would strongly suggest you link your site to an IG account. The fitness niche works great with that combination. Make sure to post regularly, build an audience first.
In regards to hosting, just go with the Namecheap Stellar Business plan. It's a cloud/based hosting, it's pretty decent, it allows you to host unlimited domains and, at $45 a year, it's pretty damn competitive.
When it comes to theme, my top choice is Astra Pro.
Why?
- Because it`s among the light-weight and fast loading themes on the market.
- It comes with a bunch of premade websites (starter sites) fully compatible with all the major page builders in the market.
- It offers a bunch of customizable features
If you need to customize the site a bit further, you can try with either elementor or with CSS Hero. Personally, I just started to use CSS Hero and it`s just amazingly powerful all the possibility it offers to customize a website without making it too slow.