We have deployed the 526 before but only in concert with the UC520. Can the Mobility Exress 526 be used WITHOUT the UC unit?
Also the building is 105k square feet - will maximum of 6 supported Access Points be enough to cover the entire area?
Yes you can deploy the Mobility Express 526 and the AP 521 gear outside of an SBCS deployment using the same configuration tool (CCA). As far as your range/coverage question is concerned, it really all depends on many factors in the environment it is to be deployed in; such as building construction (walls, concrete, metal, etc.), other wireless and RF type of interference, etc. A best practice is to perform an on-site RF site-survey as well as a review of the building construction, etc in order to best gauge your range/coverage. Using the results of the site survey and the range estimates provided on the applicable product Data Sheets and documentation you should have a better idea of your wireless coverage, however as always with any wireless deployment; "mileage may vary".