Okay, finally I can type! Info dump incoming. It's a lot, so please take your time. I could honestly write a book on the topic. This is the best of my experience and knowledge, but please just feel free to take what's useful to you and forget the rest. And don't hesitate to ask me any more questions you have, now or in the future. I'm happy to help. It's nice to have peers to talk about this stuff with!
Btw it's funny you mention your son loves Brain Candy TV and Blippi, those are two of mine's favorite shows. Along the same vein, I can also recommend Blaze and the Monster Machines and BabyBus. As for apps, I recommend Baby Panda World (the same creators as BabyBus) and Khan Academy Kids.
Math
You have a few options here. It sounds like you're right on the cusp between Pre-K and Kindergarten math. The only thing holding me back from recommending Kindergarten is the fine motor skills. This is one of the challenges of having a gifted kid - the asynchronous development.
So what I would recommend would be to shore up some of the advanced Pre-K math skills while focusing on building fine motor for a couple of months.
The first thing you might want to check out is Kate Snow's Preschool Math at Home. I don't think you need to buy it, both because your son has mastered most of the topics and also because I don't think her teaching style quite lines up with his learning style, but it would be worth borrowing it or looking through the table of contents to see if there's anything in particular you want to review/master before moving on. I have an Evan Moor assessment workbook that they've unfortunately stopped selling, but the skills they list that I think you might want to work on are:
At the same time, I'd complete just a couple of Pre-K math workbooks. I'd recommend:
So I recommend working on that for a couple of months. A daily lesson might look like practicing one skill for five minutes and then doing a workbook page or two.
Once he's a bit more comfortable with tracing, I would optionally add in:
When you feel like he can handle that level of tracing, then I think you'll be ready to go ahead and start a kindergarten program. I have a couple of suggestions for you.
My top suggestion would be Simply Good & Beautiful Math K. It's really attractive, includes stories, is light on writing, conceptually solid, just overall fantastic. Note that it does have some non-denominational Christian content.
Another option is Right Start Math Level A. You'd need to buy the Math Set just once, and then the Book Bundle for each year. This is not my personal favorite, but based on what you said about your the way your son thinks and learns, I think it's possible it would hit a "sweet spot" in his brain. Take a look and see what you think, and what appeals to you and him most. Here's a sample.
Once he's into Kindergarten math, there are lots of workbooks to recommend. Forgive me for not linking them all, but they should be easy to Google. You definitely do NOT have to do all (or any) of these, just whatever looks good to you! These are roughly in order of difficulty:
Again, at this point I would suggest one 10-15 minute lesson plus a couple of workbook pages per day. Watch his stamina and plan your daily lessons to be a doable amount even on his hardest day.
Language Arts
Alright, so you have a few options here. He's ready to start reading, it sounds like, but the problem is that blending is more of a developmental skill than a cognitive one - it comes when it comes, and it can't really be forced.
So for reading, I have two possible recommendations:
For reading/phonics supplements:
For general language arts:
Finally, something I think you could add for language arts that your son would really enjoy is some literature-based curriculum. Any of these would be amazing. If I were teaching your son, this would be my "special" curriculum I focused on, in the way I do science and engineering stuff with mine. I suggest just buying the guides and then checking out as many of the books from the library as you can, in order to cut down on costs:
So at this age what I would do as a daily lesson would be something like: