My suggestion is to grow in an organic way, i.e. try to identify some areas in Mer / SFOS that require further development and apply for several NLnet grants. (Keep in mind that maybe the funding call is competitive and it’s not guaranteed they will fund all / any. Applying is not too much effort, though).
In parallel, try to set up the organization, perhaps with help from another grant.
Both efforts will hopefully generate a bit of momentum in the community, and this can aid further growth.