Hey, dalmore!

For your commute, a folder sounds like a very good idea. I mean, with a folder, you compromise your speed (for several reasons) but gain in compactness. But it looks like you aren't going to be riding much, since commuting is almost all the riding you'll do, and your commute is only 4.5 miles one way (w/o counting the bus part), so speed, efficiency and other considerations that come with long distances are not a big issue. So the main disadvantages of the folder are not going to affect you much.

On the other hand, the advantages, which you listed in your post, are important to you. It's nice not having to worry whether somebody is picking a lock of your bike this very moment and knowing that you can always get a ride from a co-worker if you don't want to bike in the rain.

So - try it out, take a folder for a spin, and if you like the way it feels, I say go for it. There are some people on this forum who commute on folders and it works for them, so why not for you? The only issue might be the mud on the path - I don't know how deep the mud gets there and how well a folder would handle that. Perhaps people who know more about folders will tell us more. I don't know so much about them, so don't take my post too seriously, but it's just my two cents.