I'm not really sure to understand what would happen if I push to
several commit with the same Change-Id; would it create a patchset or
replace the former commits?
Patch sets within the same change ID replace each other with the most
recent one is the one being reviewed and potentially merged.
Also, even if I would probably not send as big changes as now again,
see kernel devs sending features is a series of patches for more
readability, so Gerrit is unable to do that?
It is. You just give each commit a different change id and push it as
a different patch. Gerrit knows how to track dependencies between
patches and present then in the UI.
git-review helps here - Given branch 'foo' with N commits on top of
'maser', checking out on 'foo' and running 'git review' would
gerrit patch and a change-id for each commit and would send them to
Gerrit while also setting the topic in gerrit to 'foo' to allow
looking at the patches as a group.
Please note that each commit is reviewed separately, a change
requested by a reviewer for an earlier commit may necessitate
adaptations for later patches. When submitting sets of patches one
must be ready to perform the occasional 'rebase -i'...