Thinking of converting HTML site to WordPress Blog

1. Even if I utilize search engine friendly URL’s, how will the switch affect my current rankings in search engines? I imagine adversely because my URL’s will change?

You’ll probably notice a drop, maybe url forwarding may help?

2. One thing I never like about blogs is the archive that archives articles by month, which to me would make it hard for a visitor to find something specific. My current site is set up with a specific menu that doesn’t change & I’d like to keep it that way. Is everything automatically archived or is that optional?

That is a feature. But you can do whatever you want. There are categories, tags, month, year, day, etc. The options are endless. You can organize however you want. Here’s an example page I have to help people find stuff
https://www.rvoodoo.com/explore/

3. Is it fully customizable, meaning I can keep my site’s current design unchanged (with maybe a few acceptions)?

Yup, if you can make a theme for WP that matches your current site. I would recommend googling on theme creation. WP can be just about anything to just about anyone.

4. What are the benefits of having a blog vs. a static html site?

Just that, static is static. WP is dynamic. Once it’s up and running it is simple to add content, adjust things, reconfigure things, etc. You can continue to add content over and over. And redesign and upgrade is so simple. You can add features (with code or plugin) without affecting the content, you can change the entire look and feel of the site by simply re-themeing, content remains unchanged, etc.

Ok thank you, I appreciate the response.

I have found that the word press sites have very good search engine placement.

Page names can be customized with a simple custom code I use:
[%postename%] that way the page url is named by what you name the page or post.