Category Order and Display in Backend

I have about 70 categories and subcategories and it is really hard in JEM to have them in a good order. So my questions/comments:

1) Is there a possibility to have all of them diplayed on one page (not only 20 per page) - an admin template override would be ok too, but I couldn't figure out where the imitation of 20 items per page comes from.

2) the reordering of the categories doesn't work - when I move one item with the small arrow, it moves down but, the next time the page is loaded, it is on an other position.
Or when I enter a ordering number and try to save it, it doesn't keep the position.
So I had a look in the DB: in both cases the number in the column ordering stays 0 and doesn't change.

Question: isn't it possible to use the joomla drag and drop ordering solution? isn't it a built-in feature which could be used by all extensions?

Thank you

@1 I tried and posted for venues view in administrator: You can make the same for categories, events and groups
You can make an administrator template override an insert in the categories default.php the following: and insert into the administrator language file
COM_JEM_DISPLAY_NUM="Limit"

Thank you!
Very nice and it works fine.

a propos: the number comes from Joomla configuration! You can change this in general in joomla configuration

there's one thing not so nice: the list_limit shows always "5", even when it shows 500 items! I don't know how to change that to the real amount.

This is marked as SOLVED, but it is not. The first question on pagination is solved, but the issue with reordering not working is not.

I can reorder using the arrows (changing numbering does not work), but the order reverts to it's original positions after saving. I even checked in phpMyAdmin and it all looks OK. There's something broken here.