Your experience sounds normal. I found it a struggle to find teaching in the first year as well. Often the process of filling vacancies is not very transparent.

In my experience, most of the posts are filled prior to September for the upcoming academic year, so the best time to be trying to land a post is in the months prior to this. It can be competitive, but much depends on the size of your department and what areas you are willing to teach in (In particular, students who are required to teach because of university scholarships are allocated slots first). If the department is large enough, there should be positions freed up by PhD Students that graduated during the past year.

It is standard that the module will be offered to the TA who taught it the previous year first. Although it seems unfair when you are desperate for an opportunity, once you do land a position you will be thankful that this is the policy and that there is an smidgen of stability in the whole process.

Regarding employability, i can only comment on my own discipline. If you are applying for a lectureship, teaching experience is now considered desirable. The completion of teaching modules and PG Certs are also becoming more common as well. I would talk about this with your supervisor(s), as they will be in a better position to advise on your subject area specifically.

Whilst it is evident that you have been let down by the communication in your university, i'm not entirely clear about what it is you want.

Whilst the viva went badly, you weren't failed outright. You were given an opportunity to resubmit. You haven't indicated any grounds on which this decision could be legally challenged.

Can you be more specific about exactly what the issue is. The thesis wasn't ready to pass. You can't challenge this on the basis of poor supervision, or bad advice from the Dean. The best you can hope for is the time to work on the corrections needed and an opportunity to resubmit. You were given this opportunity.

You may feel like you were given bad advice by the Dean, but i don't see that it really had much impact on the viva itself. You were ten days before the submission date. It's really too late to start flagging issues at that point. You sent your full thesis 5 months before submission, your supervisor had approved submission two months later, so what was it that you were waiting on? Was it corrections? Did you tell the dean that your supervisor hadn't read the thesis yet at the time you asked for the advice?

Yep. I’m a law PhD student 🙂