OK, a really nice clear explanations.

First thing you need to do is find the FT clubs local to you, you should be able to find them here: https://www.mfta.org.uk/

Visit a couple of them and see if you can find somewhere that suits you both as not all clubs have good disabled access.

As far as kit is concerned, long term if you took to FT then you will most likely want to change at least one rifle. You can shoot FT with a .22, but it is more or less universally shot with .177 due to the flatter trajectory / faster velocity of that calibre. That said, it is perfectly possibly for you to spend at least the first few months getting the hang of FT with a .22, we have a guy locally who is a very experienced .22 shooter, he got involved with FT and was doing extremely well, but realised as he got better that other people had an edge on him, only after a number of months did the reason for this edge become clear, he was shooting .22 and no one had realised as he was doing that well.

You don't need to get too deep into kit at this stage, when you visit clubs you will see some real rocket ship rigs, some of which cost thousands of pounds... you may or may not end up there, but in the mean time any accurate rifle, like the S400 will do very nicely. Remember that FT courses have typically 40 targets so if you are going to share a rifle, you will either need to top up the air part way through, or find a rifle with an 80 to 90 shot capacity.... or shoot a springer.

At this stage we are not going to talk about pellets, as on its own it is a huge subject, just visit some clubs, chat with the folks there, try some courses with the rifles you have and see if you like it, hopefully you will.