Oh no problem at all- my DD has speech and language issues and I was asking so many questions about that, when it’s new you absolutely want to make sure they are getting the right support.
So with TA’s I haven’t known of any who are specifically trained in dyslexia, there tend to be more specialists for ASD or EAL. They might write notes for the students, read extracts to them aloud and generally help organise their notes. In most schools TA’s are loosely allocated to specific children and part of their performance management would be monitoring how the student is getting on and whether they need any more support. Our TA’s also often act as advocates for the child and will speak to teachers directly if something isn’t working. Class teachers would be expected to adapt resources if necessary, so changing the font or the background colour or printing out additional resources.
In one to ones I focus mainly on phonics and comprehension. Half the session will be working on gaps in letter sounds (I use some methods from sounds write for this- if you have a tablet you can download) and the second half will be comprehension skills. In the small group sessions we focus more on things like PEAL paragraphs and an analysing/ expanding vocabulary.
The TA support/ teacher provision is far more important IMO. The one to one support is great, but again something I haven’t seen in any other schools. And a key factor with the one to one is repetition- so even at home something like reading eggs or similar every day would be good for reinforcing patterns and hopefully wouldn’t be too tiring for your son. And also trying to hold on to the passion for reading wherever possible- Tom Palmer is an author who writes specifically for dyslexic students and writes some football/ horror novels that my students enjoy. Barrington Stokes also have some good ones.
I would be prepared to be flexible and see how he responds in those first few weeks, then think about any amendments that need to be made to the provision. I advise colleagues that we should expect less output from dyslexic students, especially in terms of homework, as the reading will take significantly more time. Other students have benefitted just from having print outs of the PP slides rather than having to look at the board- these are both really simple tweaks to provision that can make a huge difference. So keep an open discussion with your son and see what specific elements he is finding difficult (is it reading from the board, is the workload overwhelming him, is his lack of confidence in spelling restricting his vocabulary?)
There’s a really good book- The Parent’s guide to specific learning difficulties, that talks you what to expect at each stage and conversation you might want to have with the school.
Last point (sorry this has gone on!) most teachers I work with are hugely dedicated and passionate about their students. At secondary they may not know their students inside out as they don’t have as much contact time. If they’re not making adequate provisions at first assume it is due to lack of awareness rather than anything more sinister and have a chat with SENCO/ head of year/ form tutor. The vast majority of teachers will go above and beyond to ensure you son has the support he needs to access learning.
Hope that helps- more than happy for any other questions as can empathise with how 
it is trying to work out support.
This article has written the key points more concisely
www.goodschoolsguide.co.uk/special-educational-needs/dyslexia/mainstream-schools