Combining custom WordPress blog theme with legacy static HTML site?

I have a legacy site for 15 years which is basically a large collection of articles, organized into a tree of folders. Over time, I accumulated back links from a lot of other sites, and they are obviously conventional links like

mydomain.com\subject1\article1.html

Now, I'm about to launch my new website which will still use the SAME old domain name. The new site is built on a custom WordPress theme and is blog-driven. All my new content will be frequent short blog posts, as opposed to infrequent long articles of the past. And I can re-publish my old articles as blog posts, too. So far so good.

Here comes the question. I do not want to drop my old back links dead. It will hurt my rankings and it will prevent potential visitors from reaching me if they come across one of those old back links. My plan is:

- do the normal install of the new website as WordPress theme, with the blog and the new look

- also copy the old tree of legacy articles into the root directory of the new website, just so the old-fashioned links will still find their target

- provide NO links from the new blog site to the legacy files, keeping them stealth

- but on each of the legacy articles, include a notice "you have reached my discontinued legacy site, click here to visit my new site"

Basically, I want to install a hidden closet on the new site that current visitors will not see, but my old supporters who "know" about the hidden closet will still be able to access.

Question 1: will it work, as far as preserving old links, or will WordPress somehow disable them?

Question 2: will I risk damaging WordPress theme by installing some "foreign" legacy files outside the theme?

Question 3: is there a better solution to my problem?

Thanks to all the experts!

Michael