Executing multiple rename commands with find

You don't need separate rename's here. The first argument to rename can be any perl code that does the modifications you want on the file path (as stored in $_), you don't have to use s/pattern/replacement/flags let alone only one of them.

Here, you could just do:

find . -depth -exec rename -n -d '
  $_ = lc $_; # lowercase
  s/[ .-]*[ -]+/-/g' {} +

Or if your rename doesn't support -d:

find . -depth -mindepth 1 -exec rename -n '
  my ($dirname, $basename) = m{(.*)/(.*)}s;
  $basename = lc $basename; # lowercase
  $basename =~ s/[ .-]*[ -]+/-/g;
  $_ = "$dirname/$basename"' {} +

here turning all <0-or-more-spaces-or-dot-or-dash><1-or-more-spaces-or-dash> to a single dash, but you could do all your s/.../.../s instead, separated with ;s:

find . -depth -exec rename -n -d '
  s/ /-/g;
  y/A-Z/a-z/;
  s/[.]-/-/g;
  s/--/-/g' {} +

In any case, you want to make sure the substitutions are only applied to the basename (hence the -d) and that leaves are renamed before the branches they're on (hence the -depth).

(-ns above are for dry-run).