1. How many number of users that Projeqtor can handle and how much of data it can store in database.
There is technically no limit.
All will depend on your server performance, and architecture (think about clustering for high level platform)
I have customers with hundreds of users (the most I have seen is 800 users, with 200-400 daily connections)
PrjeQtOr can handle thouthands of lines (activities, tickets,...)
2. Is this tool will workout for nearly 100 users,because I want to use it for large project.
YES !!!!
(read above)
3. In "Real work Allocation", how many users can access at a time.
Many !
As each user will enter his own work, there in no conflct to fear.
4. Iam getting so many issues while upgrading from old to new version(Iam just replacing new version files with old version files then using). Issues are some pdfs are not exporting and GANTT is not displaying...etc.
One issue has been reported on Gantt printing.
Don't hesitate to report issues : please describe use case and join projector log file