I didn't retire then work part-time. Instead, I switched from working full-time to part-time for 7 years before I retired in late 2008 at age 45.
Like you, dlgobeavs, I was greatly helped by the exploding value of my company stock. This was back in the 1997-2008 period which included the downfall of companies such as Enron and Worldcom. When I had the chance to sell some shares after 2002, I did. Still, I had plenty of shares I had to hold onto until I left the company, and I was able to cash out those shares and not get hit so hard on the tax side. Dlgobeavs, are you aware of NUA (Net Unrealized Appreciation) which allows you to sell shares of company stock using the lower long-term cap gains rate? There are some specific rules about selling such shares, so make sure you are aware of them. NUA works well when the cost (par) basis is small and the appreciated gain is big, which is what happened with me (97% NUA, 3% par).
I switched to part-time and later stopped working in large part to despising the commute, even as little as 2 days a week in the last 17 months I worked. I had already been doing some new or resurrected activities when I first switched to working PT, so I didn't suddenly have to find new things to do when I retired. (The big change was when I switched to part-time 7 years earlier,)
I agree that building a cushion into your budget is a good idea. I made sure I had that in case I went on a small spending spree from time to time. The cushion absorbed the spree without affecting anything else in my day-to-day life, something I required in any ER plan.
One part of my ER plan was to split it into 2 parts. The first part was getting from age 45 to ~59.5 using only the taxable part of my overall portfolio. After that, when my reinforcements arrive (SS, frozen company pension, rollover IRA), my picture looks only better. Do you have similar assets currently not readily accessible but will be later on?
I hope this helps.