When does government formation begin?
ERC and Junts had a first meeting already, but negotiations might take some time
Who else?
Once ERC and Junts reach an agreement, they will need to negotiate with the CUP. It's not going to be easy, because the relationship between the two main pro-independence parties is rather strained and they have differences on strategy. Junts and CUP have a rupturist rhetoric, while ERC currently supports a gradualist approach to independence and rejects unilateralism. Anyway I yhink the most likely outcome is that they will reach some compromise, because the alternative is calling a new election
There exists other alternative on paper that is politically impossible at this juncture: the PSC-ERC-ECP tripartite. ERC signed a document alongside the other pro-independence parties compromising they are not going to deal with the PSC. On the other hand, ECP won't support a coalition government incorporating Junts. So the only politically viable coalition is the one I mentioned earlier.
It is believed the Spanish government is going to issue a pardon of the Catalan jailed politicians, maybe before summer. This gesture would have political repercussions and quite possibly it's a neccessary step towards some kind of reconciliation, but the rift between 'national communities' is too deep in today's Catalonia
that is a very stupid idea