Does freedom of Assembly and association covers forming Political Parties?

Yes. In the case of Alhaji Abubakar Rimi v. Peoples Redemption Party[1], the court stated that the provisions of the constitution in this respect applies to “individual, corporate and incorporate bodies, and enables them to come together voluntarily under a political banner or leave the association as they please”.

[1] (1981) 2NCLR 734 HC