About suffering, expectations and unfalsifiable beliefs
The Buddhist problematic isn't about whether beliefs are true or false, or provable or unprovable. It's about whether we cling to beliefs, because the clinging itself creates dukkha. 

So for instance, let's take your statement: "Our true self is formless, without comprehensible features." You adopt this belief, and like it, and it doesn't seem to interfere with your meditation or other practices. Fine. But then along comes another Buddhist, who says: "No, no no: that's not right.  What I believe is this...". Suddenly you find yourself involved in an intellectual dispute, wrestling (good-naturedly) with another practitioner about whose perspective is better, and which of you has more experience to back up their view. One way or another (unless you're very careful) someone's ego is going to get bruised. And then along comes some decidedly less enlightened person who says: "You two are a pair of blowhards and it's all a crock of sh*t anyway, so stop pretending you're so high and mighty." So not only did your statement make you a target for abuse, it gave this poor guy something concrete to vent about.

Fixed beliefs — even innocuous-seeming ones, and particularly ones that are not otherwise decidable — are focal points for conflict. Just think about the Christian faith, where a fixed, undecidable belief in a loving God indirectly fills the world with anger, resentment, and hate. I'm not going to go so far as to say that a belief like this is an obstacle, because beliefs like this are useful tools at certain stages of spiritual development. But in the end, even beliefs like this will have be released.