Re: CELTA in London
Welcome to the forum, Amusicum.
I can't give much advice, but can say something about a couple of your questions.
The question as to whether you are putting too much pressure on yourself is something only you can answer. CELTA courses are hard work - but they are short and, once they are over, that's it.
All CELTA course-providers are regularly moderated by Cambridge. I don't believe that a course taken in the UK has any more value or prestige than one taken elsewhere, though non-native speakers sometimes choose a UK course for the experience of being in an English-speaking country for a few weeks. Most employers are interested in the certificate, not in the course-provider, or in where the course was taken.
Whle Cambridge ensures that all courses satisfy their requirements, one particular course may be more/less attractive to some trainees than others. However, this often depends on the trainers who happen to be running the course at the time, and there is usually no way of knowing that in advance.
Please do not edit your question after it has received a response. Such editing can make the response hard for others to understand.