Okay - firstly make sure you're using the latest version. About 1 week ago, I made some changes to fix some issues with Nucleus integration. (nothing that Nucleus had done wrong, just my mistakes.)
So, ya, use the version released on the Ore page.
That should fix any issues with prefixes and suffixes.
Also, make sure you're using the correct command.
/luckperms group admin meta addprefix 100 "&a[Admin] "
I know it's a bit confusing. Basically, the 100 above is the prefix's priority. When considering which prefix to apply for a user, the plugin will gather all of the prefixes they have and inherit from other groups, and select the one with the highest priority.
(I'm also aware the wiki page is outdated on this. I changed the command layout earlier this week and haven't had a chance to update it, so apologies for that.)
Regarding setting the default group: I encourage you to read this wiki article. It's a bit complicated, but it will hopefully make some sense.
Basically, all users are a member of "default", unless you setup a rule to change that. I strongly urge you to just use "default" as your member group.
And finally, to setup inheritance, you would do the following, in your case:
/luckperms group supporter parent add default
/luckperms group moderator parent add supporter
/luckperms group admin parent add moderator