1. can more than 110 000 users be imported
This should not be a problem.
2. My website runs a specific version of phpbb SEO for allowing permalinks for every forum – will this be imported ? (so that there is not a lot of redirect)
No, these will NOT be imported and you will need to manually set your permalinks and make some redirects using .htaccess
3. My website stores custom profile fields for every user (more than just ICQ, but also custom ones). How could I have the same kind of functionalities using bbpress ?
Currently when importing from phpBB we are importing and storing the default phpBB user fields as outlined here. You could modify the import script to include any of your custom user profile fields so they also get stored in wp_usermeta.
After that you would need to find a WordPress plugin that supports extended user profile fields to utilize that data. I am not sure of any specific plugin that can really do that out of the box with bbPress at the moment but at least you ‘would’ have all of your users advanced profile data stored.
4. What about performance – will it be better than phpbb. I know bbpress is very powerful for small forums, but I have no idea regarding huge ones. Can wp caching plugins work for bbpress as well ?
There are some large sites running bbPress and I would suggest you setup a test site to see how it works for yourself personally.
As to caching it appears that ‘WP Super Cache’and ‘W3 Total Cache’ do not work well with bbPress as discussed in this topic though there is ‘Lite Cache’ which appears to work with bbPress as per this topic.
5. Is the entire UI translated in French – it doesn’t seem to me, but maybe I’m wrong.
The current status of the French translation is at 11% translated with 879 strings untranslated though 734 of those strings have been translated and are waiting for the fr_FR translation validator to validate the translations.
https://codex.bbpress.org/bbpress-in-your-language/
6. Can I use any plugins writter for wp for bbpress ?
I am not sure what you mean for this question
Any more questions please ask away…
