1. I'd like to know what your thoughts are about the importance of sequence of returns.......
You've done your homework well. Sequence risk is real and can be huge. For example, our financial plan allows for a 40% reduction in networth due to this issue. That sets the minimum amount of fixed assets we hold - we hold enough cash / bonds to use as spending $$ through a typical downturn (3yrs+) so we don't have to sell equities at a big loss.
The important points are (a) yes, this is a critical risk and (b) have a realistic action plan for what to do if it happens. At your age/situation, a plan may simply involve working longer now to save more assets. Or could be taking on part time work if needed in the event of a downturn. As long as you are monitoring the market and have a real backup plan in place, the risk can be mitigated.
2. If the markets do drop, do I ......... How do people manage withdrawal rate?
If markets drop, activate your backup plan. The goal of the plan should be to NOT sell off your equities during the downturn at a loss. In our plan, we have enough fixed assets to ride out most downturns without cutting expenses. Second step if needed is to cut expenses. We could cut 30-40% without much pain. Last step (extremely unlikely for us) would be to find a way to get some income to help preserve assets.
3. If anyone has a similar financial situation as ours (source of income exclusively from market investments), I'd like to hear your thoughts on early retirement. How are you managing your withdrawals?
We have significantly more assets that you so not similar. But when looking at your numbers in Firecalc and seeing the thought that you have put into your plan, I'd say firm up your plan and go for it. Just make sure of a couple things.
(a) have / or develop a backup plan in the event of a downturn.
(b) watch your expenses VERY closely since you are tying yourself into many, many years of a very low budget (at least relative to what I'm used to).
(c) watch your wife's pension situation, make sure if they go bankrupt or look like they may cut benefits, you adjust your plan for that.
(d) make sure that some of your Firecalc runs account for the possibility of one of you passing early. You'd lose one SS benefit then. Probably not an issue for you but worth double checking.
(e) consider cost of health care if you need it in other countries...ie, if you end up needing expensive back surgery (for example you tripped and messed it up royally), figure our if the local country has facilities you can use and can you afford it .... or do you have to fly back to the US to our expensive options and use them. You have many years when such things might happen so worth starting to get a feel for this. Some here on this board have mentioned using facilities in other countries quite successfully and quite economically. May be worth another thread if interested in this.
Good luck to you and happy travels.