Upgrading Drupal

Hi,
This is my second attempt to upgrade my Drupal 7 to 8(.6.4) and I have some questions:

Between the first and second upgrade attempt I changed my drupal 7 site and removed all LinkImage fields in the different nodes I have and changed them manual to 2 fields a image an a text field with the Url, so in the view I could make a rewrite results in the view which places the Url on the Image, this works on my drupal 7 site.
Took a few hours and maybe this could be done with an handwriten upgrade, but It's done

Hey,

I have made a map view to show a huge amount of location content, i have over 1700 content items. It is far too slow, im looking to increase the speed at which the map can load items based off their proximity to the client. Im not sure how to do this, and any help would be deeply appreciated

Greetings-

My site isn't complex. It has a couple of content types that are little different from the defaults. I've added a few contributed modules, but not many, and I've now removed those that may be problematic. The theme is basic Bardik with nothing but a color change. I have changed some menus, but nothing much - this was meant to be a temporary site until I moved to D8 and rethemed with Twig.

So I ought to be able to migrate to D8 easily.

Apparently not.

Hello!

I have installed Drupal 8.6.3 some weeks ago and after updating to version 8.6.4 i am not able to open the page anymore. I am using XAMPP and deleted all folders and datas besides "Sites" inside my page folder. After that I pasted all folders and datas of the new version, like it was explained on the Drupal Page. Now I cannot open the page anymore and this message is shown:

Additional uncaught exception thrown while handling exception.

Hello!

I have installed Drupal 8.6.3 some weeks ago and it worked normally. After following the instructions for an upgrade to the newest version 8.6.4 i cannot open the page anymore. For updating Drupal from 8.6.3 to 8.6.4 i have deleted all files of the old version besides the folder "Sites" and pasted the new unpacked folders and datas of the new version (besides the "Sites" folder), like it was told on the Drupal Page. I am using XAMPP for that. 

While opening the page with the new version i am landing here: