Review – Usability of ERP system [on hold]

As part of my master thesis on ERP Usability study I have conducted survey based upon the SUMI (Software Usability Measurement Inventory) questionnaires which involves five aspects efficiency, affect, helpfulness, control & learnability for which I received 50 responses and now I need to conduct 10 expert interviews which should be relevant to the SUMI methodology.

Could you guys please review my questions and suggest me new questions or changes be made to the following questions:

Were there any usability studies conducted while piloting new ERP within the company? If yes, what were the main areas of interest (particular parts of user interface)?

Is there any convenient way to customize the user interface of your
ERP? If yes, to what extend

Were there any workshops facilitated after ERP was implemented? If
yes, what were the main topics of the workshops?

Are all users satisfied with the chosen ERP system? If yes, what do
you think is a reasonable time that took for users to adopt / adapt
to the ERP system?

How easy was it for you / users to learn the ERP system? 

Do you know why did your enterprise decide to purchase particular
ERP If yes then why?

Do you or your organization consider the importance of Usability
Features while purchasing ERP system? Yes, No, Do not know

If yes,could you list few Usability features which you find are most
valuable?

What do your users and/or you like about ERP system? (Learnability,
Error support, Presentation, & Efficiency) 

What do your users and/or you dislike about ERP system?

What are the biggest challenges in terms of usability of the ERP
system within your enterprise?

What are the critical incidents" (i.e., serious breakdowns in
human-computer interactions) encountered by users or noticeable
breakdowns in the user’s performance?

What action was taken by the management to address such critical
incidents instantly?