it's the best version of Elgg 3.x ;)

What kind of answer do you expect thinking about your question a few days ago https://elgg.org/discussion/view/2972868/suggested-stable-version-for-elgg

Yes I hope this is the best version. But will it support existing plugins? because if I pay attention the plugins that are here only support versions 2.3 and 3.0

There are fewer plugins available for Elgg 3 than there are for Elgg 2. As the plugins written for Elgg 2 won't work without changes on Elgg 3 in most cases you can't use the plugins not yet compatible with Elgg 3 on any Elgg 3 version.

Now it depends which plugins you need - and if you really, really need them - if it's an option for you to start without these plugins for now and start with Elgg 3 or if you need these plugins in any case and therefore have to start with Elgg 2.3 for now. If the plugins are updated to work on Elgg 3 you can upgrade your site at that time. But it's kind of impossible to give any timeline when developers might publish updated versions of their plugins. For example, I would have thought that I would have finished upgrading all the plugins I maintain already but I just haven't found the time yet. With some other developers it might be the same. But in some other cases the developers might have abandoned their plugins and won't make any further releases anyway. So, it depends on the plugins you need / want to use what Elgg version would be best to use.

It seems the counter plugins available haven't been updated for many years and therefore very likely won't work without some changes. Maybe it helps nonetheless for you to take a look at the code of https://elgg.org/plugins/421112 and https://elgg.org/plugins/872625. The "Westors Download Counter" plugin appears to offer what you are looking for but it's for Elgg 1.7 and older. The "Views Counter" plugin is not exactly for counting the downloads. But it's supposed to work up to Elgg 1.12 (maybe even Elgg 2.x with some minor changes). So, the "Views Counter" plugin might be of some use in learning how to get the "Westors Download Counter" updated.

You can use code from the community plugins

Is the non-responsive friends picker just not a problem for everyone else? It was for my users, when I was running an elgg site.

this kind of friends picker existed in Elgg 2.3, but in Elgg 3.x this has been changed into a different way of managing users and user/friends lists. This plugin makes no real sense for Elgg 3 as far as i can see.

AH IC, I have been and am still having trouble with the 3,x installer. It fails with, "installer failed at:
"An exception occurred while executing 'SELECT * FROM elgg_config': SQLSTATE[42S02]: Base table or view not found: 1146 Table 'XXXXXXXXXXXXX.elgg_config' doesn't exist", after writing "elgg_migrations" to DB.