Building these at the same time as doing the project will add significantly to both the cost and the risk. Using relatively new technology is riskier than using old technology. You should only ever consider this approach if the technology proposed is vital to the delivery of business benefit and this benefit can not be achieved in any other manner. Using unknown technology is fine for pioneers. It's amazing how many companies, with no record of project delivery, set up a brand new team to deliver a project and expect them to perform like a seasoned group of hardened project professionals.
Success breeds success, teams that have already delivered are more likely to repeat that success.
New teams are an unknown quantity. The more things you change, the more complex things will become, and this increases the risk to the project, reducing the overall chances of success. The fewer the variables the better. The lower the more parties you have to co-ordinate the higher the chances of failure. You can either accept an estimate at face value or check to see how the estimate was developed.