I would say that #2 and #5 can be the most costly and are so easily avoidable.
First with #2, just do your “due diligence.” Ask your realtor, you already have a relationship with him/her and they probably have a list of resources.
With #5, it’s super easy. Take a breath, don’t be in a rush. I know it’s easy to get caught up in the excitement of a new home but living in it and seeing how you use each room before blindly marching into a renovation will save you tons of money later. And hire a designer! They can save you from many pitfalls that will inevitably come up.