The one thing to decide is what you are intending to ride. Triathlon, check the rules, they were trying to adopt UCI rules at one time, but this doesn’t seem to have happened at the typical competitors level. Ironman are a complete outlier from rules and regulations.
CTT have got some rules on position and kit - again, check.
Not all CTT bike set ups will be UCI compliant. If you’re likely to ride a UCI event ( which could include some Scottish time trials in theory, but also events like the Duo Normand, or the UCI amateur events like the time trials in the UCI World Series).
In practice, the higher up the finishing order and level of competition, the more likely checks are.