I migrated from MT to WP last spring. I'll try to answer you questions.
First of all, I was troubled by this statement:
If I do, I can no longer get MT without paying for it, so I"d prefer to switch to WP.
You can still get a "dummied down" version of MT 3.x, for free, but it won't have any tech support (isn't that what the forum is for anyway), and you are restricted to only one author and only three blogs. Download it here.
Now, if you still want to migrate to WP:
Is it hard to switch from MT to WP?
PapaScott has an MT to WP conversion script that I have successfully used on my own site and on several of my clients' sites to migrate MT entries to WP. The comments can be dodgy, as some of them ended up on the wrong entry, but that was easily fixed. Overall I was pleased with how the script handled the conversion.
I'm a CSS HTML moron. Can I use the same template?
It **can** be done, but it's probably just as easy to go ahead and modify the CSS file that comes with WordPress, keeping the WordPress elements as they appear in the index.php file -- which other than your comment boxes, is the ONLY (yes, you read it right) template you really need to change in order to use WordPress. One template. Of course, if you want other static pages on your site, as I and many others have, you will want to make a copy of your index.php file once you have it the way you want it, and modify it for those extra pages (e.g., About Me, Contact, 100 Things, etc.). Hopefully this will make sense once you download and install WP and start working with it.
If you need some tutorials regarding working with WP templates and the stylesheet, check these out:
BlueBird Chronicles WP and PHP Tutorials
WP Modifications from Burning Bird
That should get you started!
Are there any hosts that support WP that anyone can suggest?
Almost any web hosting company that offers PHP and MySQL can support WordPress. I can recommend the following which I know to support WP; others will probably be along shortly to add more choices!
(my blog and five of my other sites have been hosted here for four trouble-free years)
2. My own web hosting service with very generous bandwidth limitations
3. Global Internet (where my web design site is hosted)
Hope this helps and hope you decide to go with WordPress!!