. If you've already got the TR visa, you've done the right thing, the STV is a crap alternative. The COE doesn't indicate visa type. You'll get stamped in for 60 days, with an option to extend for a further 30.
In relation to the PR question, an ex neighbour of mine went down this route, and application was rejected because of a 60-day break in the three year qualifying period. As Benjamin has pointed out the criteria (unless it's changed in the last 18 months) required three consecutive annual extensions, so if you take a 60-day extension, the clock on PR will be reset.
Airlines and immigration are both aware that many people will extend, and you will find that on onward (not necessarily return) ticket outside of the 45 days, but within the 75 days will be accepted.
Andy Crocitto. I didn't notice any lecture from Stan, I think he was merely pointing out the correct terminology. Thai visas/immigration is a very complex monster and it is better manoeuvred when people are very clear on the approach. Too much incorrect information is given on Facebook groups and if not corrected it can "snowball" and leave people in a quandary. For example, your advice that a "return ticket" is required is totally wrong. What is often needed is an "onward ticket". My advice always is not to criticise those trying to help, and that small corrections along the way can help people understand the topic more clearly.