In short. Overwhelmed. Hadn't expected the answers I got really.
I had to leave most of my tools behind when I moved, so am kinda starting again from scratch. I have a very small subset of tools available for use at the local Hackerspace, but on the whole the quality is not great (I binned 2 squares last week when I realised they weren't square, and I didn't want anyone else wasting materials). So it means that I'm looking to buy tools to use for this project. I don't have a plane, and I left the mitre saw behind (having concluded it was crap). The chop saw I have access to at the hackerspace is not accurate, it's been used and abused by too many people. I do have access to a table saw, and a router table. The table saw can cut 90° only. A suggestion from a friend here was to use the router table with a 30° bit in it (
https://www.ecotools.nl/hm-fasefrees-35-mm-30/). If I cut the wood to a 90° angle with the table saw, I can then impart the angle with the router bit. Touch it up with sandpaper, and it should give me the angles I need.
Taking evening classes in Carpentry are not really an option, so learning how to use a sounding board (I had to google that to find out what it is), unless through books or youtube is not going to be easy.
You've all given me lots of answers, but I'm not sure I can pin any one of them as "Aha! that's the solution". All of them require a massive out lay on tools for what I thought would be some simple cuts. I had half expected a "Yeah, that saw sucks, but this one here which is 3x the price is what I have and it works good", or "This mitre block for €30 on amazon should get you pretty close to what you want...". I think this is largely down to me asking the wrong question.
Things like the making a plane work for the task looks like it would involve buying a plane, some waterstones and a grinder to sharpen it, and then the materials to make a sounding board. While these are all tools I would like to own in the long run, it's a big outlay, and any tools I own I have to transport in a backpack on a bike too and from the workshop. Not to mention it kinda takes the momentum out of the project if I have to sacrifice a few days to learn a tangential skill, and make the relevant tooling. Again my bad for asking a poorly worded question initially.
Thank you all for your answers, sorry I asked such a poorly worded question in the first place.
J