Convert parent site (1&1) to WP w/o harming existing WP blog in subdirectory?

Hi all,
I hope this is the right forum to post my question in: I’ve currently got a WordPress blog within my 1&1-hosted website, which is built on MODx. I have two separate databases, with the blog installed in subdirectory ‘https://www.soulambition.co.uk/blog’, accessed by clicking ‘blog’ on the top menu.

I want to switch the main site to WordPress now too, and think I need two instances of it. I could perhaps expand my existing one instance of WP, using static pages for the Soul Ambition info stuff, but then my top nav would have way too many entries – I need a separate menu for the website and the blog. (Soul Ambition menu has “home / coaching / training / words / video / wheel of life / csr / testimonials / contact / blog”, the blog menu has “home / hello” plus category pages “arts / business / careers / personal / social media / travel”). So I think I need to use two instances of WP – installing a new one with static pages replacing the pages of my current site, and keeping the existing instance for the blog.

My question is, if I install WP on my main site, which I think will overwrite my main SQL database, would that also overwrite the existing blog? Since they’re two separate databases, I’m hoping not, but want to be sure! If it doesn’t overwrite it, would it overwrite the link between the two?

And actually, I use a different name for the blog once someone clicks on it – the blog title is “Dream It, Do It, Love It!” as opposed to “Soul Ambition” but the URL is https://www.soulambition.co.uk/blog – so maybe I could have 2 entirely different domains (tho’ https://www.dreamitdoitloveit.com isn’t available), with a WP installation on each. It seems simpler to me to migrate the main one, but am I missing a trick there?

I’d really appreciate any help or advice on this – I’m not sure how best to proceed!

Thanks in advance for any help,
Tracy