When you say 11px, you really mean 11pt, right? Font sizes are specified in points, unless you're working in Photoshop...
Yes, in InDesign the difference is academic, but it's still worth checking...
On my InDesign its showing me px not pt ? Maybe thats something that can be changed. What size and font would you sugguest?
Actually thats funny because I have pt in Photoshop and px in Indesign ?
Sounds like you set up for an interactive document rahter than for print in the initial setup. No major harm done. Right-click the squer inthe upper left corner betweenthe rulers and reset the units to inches and see if the type reverts to points, if not, you may be able to change it in the prefs, and failing all there is a 1:1 relationship between px and pt in InDesign.
None of the above has anythign to do with your question about suitability. There's no good reason I can think of to choose Arial over the Helvetica Neue in any size. And I don't think there are any "standards" for how small the type should be. Are you expecting your readers to be older and have difficulty with small type? Will everything that needs to be on the pages fit at 11 pt? I would advise using the larger type, if possible, to help the vision impaired, but I also suggest you print a few pages and look at them in both sizes. Are they readable, or does one look like a sea of gray?