2. What would be a good namespace for those plugins? Would
Mojolicious::Plugin::XXX::NameOfThePlugin be OK? (with XXX something personal)
In a word 'yes' it is a bad idea
is a good place to check such things.
Personal namespaces are to be avoided except where there are encouraged
Such as in Dist-Zilla plugin bundles
I might be acceptable to but all of you stuff in a top name-space like Mojolicious::Che or alike but then I dont' control it
If you sure that your modules has no value outside your projects,
cpan is not right place to store them.
You could use darkpan to install your local modules, centralize updates and so on.
Such modules can be installed via cpanm/carton/carmel
See https://metacpan.org/pod/Carton#Specifying-a-CPAN-distribution