there is no way to completely hide some items from the users, might be a good idea to add.
what we do (and with good response) is working only with "virtual report suites (VRS)". those are basically "ordinary" report suites, but with some advantages:
add segments: if you have default segments that need to be applied to almost every project, add it as filter to the VRS. that means, every new project starts with filtered data, no need for end users to apply those segments
restrict items: you can "curate" items that are visible to end user at first glance. that means if they open a new/existing project, they will only see the selected items. this helps a lot especially for beginners. but: there is a button "show all items" and if user clicks, he can see everything. we normally say "use at own risk, not confirmed to work!"