nice insights, If I may add probably these things could help too :
a. The developers, you can do some check and re-check regarding team members and developers or any information about them. If it's reliable and makes sense it can be a good sign
Developers are very important if they are reliable then the project is in good hand, you can
take them as a little assurance the future of their creation is very possible to succeed.
b. How precise the roadmap and reality or may I say the achievement. A good developer usually will try so hard to make sure the road map is fulfilled. Even though it's not 100% precise, at least it's not that far from the road map that has been planned. Good developers always attract people to invest.
Roadmap is your main basis if the team is true to thier set plans, if they keep progressing and
from time to time they are providing updates, it's also a good sign that the project will manifest.