Should I join the group now?

The disadvantage of joining a group early is that your cohome may take a long time, not to mention energy and money, to materialize. The advantages are that the earlier you come into the group, the more opportunity you have to be a part of the design and planning. And you get an earlier place in the order in which units will be selected. Also, in many groups there is a financial incentive for joining the group early in the way of a discount applied to your final house price.