I am into my 8th year. Time, job, money and family didnt allow me to do it all at once. It is a HUGE commitment, and trust me on this, there are consequences that are not forseeable. I learned the hard way.
I went with several different outfitters, for Everest, elbrus, vinson, and kili.
Denali, and Kosi I did myself.
Aconcagua I used an outfitter for mules, gas, and transport but did the mountain solo.
Vinson and Kili require guided services (ALN wont let you do it on your own, I tried, and Kili it is the law).
9k is about right for gear, and I am still using all of my original stuff, some of which has alot of patches and fixes on them:)
I honestly think, and Harry can chime in here, that for Everest you are going to really need to consider going guided. It is a complex undertaking and the upper slopes dont have any pity. In 2007 when I made summit, there were an number of unguided, on thier own groups and I didnt see any of them above 8300m camp. This of course is going to add tens of thousand to your calculations.
Not trying to disuade, just being real. I know the desire and the dream. Live it! it is a worthy life goal.
Do the kosi version though. Carstenze is not the true 7th summit. HEHEHEHEHEHE here comes Harry:)