You posted in the right place, PiNet doesn't have its own forum, but generally I keep an eye on the Raspberry Pi Forums. There is also plenty of other ways you can get support as well
As for the questions
Make memory split changes
Perhaps change the resolution to 720p from 1080p
For these, you need to be running PiNet Jessie. 1.1.8 is the old PiNet Wheezy. When you open PiNet it should prompt you about the upgrade, if not, you may need to switch your release branch (in the Other menu) to Development branch. The most recent PiNet Jessie release is 1.2.9.
Find out why our Minecraft worlds don't show up.
This is an interesting one that has long been an issue with PiNet. My understanding is it is to do with Minecraft Pi itself and its expectation for the user to be "Pi", but I haven't dug into it much given the same world will just load back up if you hit create new.
Remove icons from the desktop
This isn't an easy one, PiNet assumes you want them... In general a majority of teachers I have talked with prefer having them so it wasn't removed when the Raspberry Pi Foundation removed them.
Easily remove packages
This one also isn't easy. It is on the todo list to have a nice way to allow them to be removed, but I just haven't got to it yet. Joys of having such limited time already. What software were you looking to remove?
If you have any other queries, feel free to let me know!
Lead developer of PiNet, a free and opensource centralised user accounts and file storage system for Raspberry Pi classrooms used in over 200 schools across the world.