Does anyone have any particular recommendations for any particular Photoshop course? Over the next three or four months I'm going to have a lot of free time that I need to fill. I figured some of this can be spent refining my skills.

I've been using Photoshop and Lightroom for 5+ years, and while I'm competent with the programs, they are capable of exceptionally more than I'm able to do.

I'm looking for something that is an instructional course, and would prefer something that give you files to work with and "follow along".

Is Kelby One the best option? Any feedback on it?

Any recommendations for something similar but with an emphasis on Graphic Design/Illustrator.

Personally I just watch a ton of stuff on youtube and pick one of my similar photos to try it out.  Phlearn and Tutvid have some good stuff.

I've been doing that up to this point, and it's been super helpful, I just think that I would benefit from linear instruction.

Years ago I learned with "photoshop wow" it came with a cd and you did exercises and built your skills up.
I also had an adobe book that was a how to with a Cd and lessons. That is what I started with back in '95

Look at your local community college or tech school.  I pick up 2 Photography night classes this semester.  They were 1 night 4 hrs long each.  Cost for me  was $25.00 each.   I am a old fart so I got the old fart discount.

I don't think PS lends itself to linear instruction

learning what you need to know - as you need to know and implement it -  is most effective IMHO

example - if you need to edit landscapes, there's virtually nothing about portrait retouching that will be of much use to you

A couple comments/suggestions.

Skip going deeper into PS. If you have been using it for 5 years (for general photo stuff) and are looking at Design, you really, really need to learn Illustrator.

Don't get me wrong, learning how to successfully edit, remove, or create compositions in PS will be worthwhile, but you will spend 95% of your time creating in Illustrator.

For linear (long) courses I would recommend Lynda.com.

Thanks for the recommendation.

I'm actually looking at advancing both skills, in separate manners(editing photos better in photoshop, doing design in Illustrator).

The few times I've used illustrator it was apparent to me I had no idea what I was doing.

Photoshop is one of the most difficult programs to learn. No fast learning curve that I know.
In addition to skills with the brush, there are filters, layers and masks to learn. Plus changing from RGB to LAB color can make an entirely new set of problems and scenarios.
A text on masks, another on filters and layers, and another on LAB color together can get you up and running.

I have been watching phlearn on YouTube.  His videos are explained clearly and to the point.  I know he also offers longer paid courses on his website.