Hiram Gutierrez is the name I believe you are referring to. He is an absolute wizard with the 4L60e. His y-tube video is 2+ hours detailing a full rebuild. He talks through all of the decisions, and explains everything. I have rebuilt a few 4L60e transmissions, and I use Mr. Gutierrez' video on teardown and rebuild. For anyone attempting this, take LOTS of photos of everything including orientation of parts. As far as the naysayers go, rebuilding an automatic transmission is a very detailed procedure. If you are not a very detailed person, DON'T do this. On the other hand, if you are detail oriented and enjoy the challenge of learning new automotive procedures, there is no reason not to try.
As for special tools, yes to the teflon seal installation gizmos, yes to the shop press (for heaven's sake, don't use a hammer), spring for the replacement separator plate if your check ball has begun wearing into the plate. It was less than $30 on my last rebuild. If you're doing an "e" transmission, replace the wiring harness and both shift solenoids. (You only want to go in once.) Some say replace the sun shell with the heavier unit. It's around $60. Your money, you decide. I've never upgraded my servo, but I've always done a stock rebuild for a stock application. I don't tow heavy trailers, and I don't race my truck. Again, your money, you decide. Always replace frictions and steels. Not doing so would be like tearing down an engine for rebuild and not replacing the rings. Just don't. Last time, all in I had about $800 in the rebuild with torque converter. And yes, you can use a pressure washer to clean the case. Just blow out all of the oil passages with compressed air, and lubricate with WD-40 for good measure.
Global Transmission sells everything you could possibly need. Kits are available, and tailored to different needs. If you need individual parts that are not included in the kit, they will have them. Only issue is, if you screw up a bushing and have to order a new one, shipping will outstrip the price of the bushing. But that's true with nearly everything these days. I actually have made a friendly acquaintance at a local transmission shop. I did the same "bump the table and everything goes flying" move with my valve body. No two drawings on the internet showed the same orientation, and none looked exactly like mine. I walked in, showed them where I goofed, and in 10 minutes they had it together. They charged me nothing. I offered to pay. They said just be sure to come back to them if I needed service. And I will.