Frank,
Occasionally I start a post with a qualifier like "take this with a grain of salt since I am not in your shoes, and don't have all the facts". This is definitely one of those times.
I will tell you that if the offer is as described, I would estimate that it would raise my take-home by about 40%. Not knowing your numbers, I can't say, but I would bet that is not too far off for your estimate. That is also the easy part. The tough question is exactly what are you giving up in return. The answer of course, is lots of control and autonomy. Just how much is hard to say.
Just to give a couple of examples:
1. They cover "everything else". So you decide you want a new computer for your office or a new desk chair, or a different EMR, etc, etc. Do you just order it, and they "cover it". I doubt it, but if so, get it in writing. There will be a million questions like this.
2. "I control the employees; they pay for them". So if you want to give an employee a raise, they just pay it? If you want to hire/fire, they just let you do it? If you decide you need an additional staff person, they hire them? Even if the answer to each is "yes" (and I doubt it will be) the dynamics change instantly when you are no longer their employer.
3. You decide you want to do some marketing, e.g. a practice website. Who pays? (in other words, what about practice expenses that are not anticipated going in)?
4. If you have any other sources of income (clinical trials, etc) be careful that the contract doesn't prohibit you from continuing them (or using your office for them).
These just scratch the surface of issues you should consider.
We are going through another cycle of practice take-overs by hospitals. Hospital administrators always believe that they can run our practices more profitably than we can. Sometimes they are right, but often they are not. When they are wrong, the cost for both sides may be high. This time it appears they have the federal government backing them. On the other hand, the last time around, it often didn't work out. In our area many of the practices that were bought by hospitals (or the organizations they created for management) are now back on their own. s/p a lot of cost, stress, and aggravation.
