Filing Utility Patent on my own makes sense...yes? And when can I sell?

I have been trying to learn all I can on filing for a utility patent, and doing so without a patent attorney. I am sure (since there are patent attorneys that visit this site) that this idea would be met with skepticism and forewarnings of dire failure. Thank you for being concerned though.
My question is fairly simple, no doubt, for anyone working in the field or even those who have done so before:
-It appears to me that my initial financial requirement would be in the neighborhood of $600 to file, which would cover the filing fee; search fee; examination fee and depending on whether I did it online or on paper.
-After that, I then will wait for the patent allowance at which point I will need to pay in another $850, roughly.
-From there I make a "maintenance" payment at the 3.5 year....est. $600; 7.5 year...est. $1,425; 11.5 year...est. $2,365....."Small Entity"
There are surcharges for being late, as well as charges for multiple claims and so on but lets just say I am not late nor making multiple claims....
---Doesn't it make more sense to do it this way as opposed to plopping down thousands of dollars into the lap of a lawyer making him the first to profit nicely from my endeavors? Granted, you will need do your homework to insure protectability, in which case I am happy to take the time to assure myself that this is done.
If I have this all misunderstood please do inform me!!!
Thank you
Barry
aka hungrrrry

P.S. While I wait for that patent allowance, am I correct to assume that I am protected from the intitial filing date? Or the date mailed? From the moment I send the filing out whether online or in an envelope, is there a period of time in which to wait before I can seek licensure or outright sale of ownership rights to that intellectual property?