They have moved the Expo around on dates so it is hard to generalize that the parks are crazy as a result. In 2019 the parks will be a challenge because it is after the SCAP blockout lifts and that will put the Expo right in the path of a bunch of local AP holders scratching and clawing to get into DL because of the new Star Wars Land. It will be a hurricane and no way to avoid - so just make the best of it.
Really, I would skip Knott's Berry Farm if I were you. If you have an extra day go to the beach - either right onto the sand and into the water (Newport or Huntington?) or find a nice boardwalk or pier (Newport or maybe Santa Monica Pier or one of the LA beaches like Venice - LOL, I have never been to those beaches) and go for a nice long walk and do some shopping.
I am not the best one to ask about "what I do" as I have lots of family in the area and used to live there. For someone like yourself, take some time to see part of SoCal and please do not spend all your time at theme parks. Yes, for WDW vets, I get it. But California is not Florida. Looks like you have been to DLR before so you have at least some idea.
For the Expo, plan to dedicate your time to the Expo. Plan to get very little sleep and wait in lots of lines - way more than at DLR or WDW. Bring reading material and snacks. Get a hotel near the Expo. A good option if you want to do parks and Expo and do not want to switch hotels is the Candy Cane Inn. I did my first Expo from the CCI and it worked out great. I would plan to visit the parks a day or two before the Expo then a day or two after. Give yourself a break from the parks and all the energy of being in the park.
Hope that helps!