Wordpress websites are highly customizable.

That being said, I do side with some of the comments down below.

It's going to take some practice and patience before getting your site just the way you like it (it's not going to look perfect when you first create it, but will evolve more to your liking as time goes on and you become more familiar with setting up your website and all that you can do).

Also, be sure to follow along with the training. This will not only produce you with a great looking website, but one with a solid foundation that's geared toward success.

Let me know if you need any help, I'm here for you

Very much possible

Yes you can!
Follow along with the training and you will soon have a great looking website!

Yes it is possible but it does take time and practice

I would focus on one or the other.

Fitness and nutrition go hand in hand but when selecting a niche it's better of to specify one when starting out - you always have the option of expanding later.

Fitness and nutrition are very broad topics, be sure to narrow these down as well.

For further help on narrowing down and determining your niche, I would visit this extremely helpful tutorial: Introduction Let me know if you need any further help with this :)

I think you will do fine. Just create quality content. I would get the site built out a little in each category and like you point out add to each one in a cycle. You might want to pick one or two main topics to focus on and the rest will help bring in other visitors. Just make sure it is all quality content