Look at this thread for peoples expenses as the years pass
How much did you spend in 2010?
and search for similar threads from earlier years.
Knowing your expenses in DETAIL is one of the key things to successful ER - not only financially, but also for peace of mind. If you are not recording every $ of expense, start now & build a history so you can look at any new expense in relationship to past experience.
In my experience, getting off the hard-work-grind is not difficult if you are curious and have some interests outside of work. It is harder to accept the loss of status (or whatever you want to call it). You are no more an executive, owner, manager, engineer or whatever-you-were that commanded respect in an organization. In social settings, you'll hear people talk about work & you may find yourself giving them advice. But, you're not in the game any more, and your input will not have the same weight as it once did (irrespective of the accuracy of what you're saying). That is hard to see and accept.
On the other hand, your stress levels will fall drastically. You'll have the time to take care of yourself - health, food, family, friends, spiritual, community - you name it, and you'll have time to do it.
Once last piece of advice. Don't over commit your time. Relax for a year or so and then decide how you want to divide your time - if at all.
All the best. The best years are ahead. Always ahead.