- You can perform ETL and some cleansing with the Qlik script, although it is not Qlik's core functionality. Details here: http://help.qlik.com/sense/en-us/online/#../Subsystems/Hub/Content/LoadData/UseDataLoadEditor.htm
- It is customizable, check the APIs available at http://help.qlik.com/sense/en-us/developer/
- The code is not available to change. There is an open source community at http://branch.qlik.com/
- Check the system requirements check here: http://help.qlik.com/sense/en-us/online/#Introduction/SystemRequirements.htm%3FTocPath%3DWhat%2520is%2520Qlik%2520Sense%253F%7C_____1
- For the skills, check here: http://www.qlik.com/us/services/training/skills-assessment
- For everything else in your post, please refer to http://help.qlik.com
If you know Qlikview than it will be easy for you to learn Qliksense...
-Backend is same as Qlikview.
-Front end is different bcoz qliksense is designed in such a way, kind of user driven.
-No java script not mandatory to start with qliksense .. java script used to designed your own API through workbench.
-Look at the videos available for Qliksense Qlik Sense Forums
-Yes there is pre requisites to install this software like 64-bit OS window mandatory and for Server pls check documents.
I created a Data Quality group to discuss topics around DQ. You're welcome to join!
What do you have in mind with Thesaurus capability in terms of Data Cleansing? QlikView script provides a very powerful mapping functionality (ApplyMap, MapSubstring). I could imagine this would be helpful.