As of now there is no limitation in the free plan in our SaaS offering, neither for projects, disk space or members. This was not the case in the past, and this will not be the case in the future.
We are working to have a fair and interesting offering, with different options both on our SaaS (https://tree.taiga.io) and for people who want dedicated and on-premise instances.
To be more concise, the answer to points 1 to 3 is “Not as of now”, and the answer to 4 is “No, and it will indeed change”.