Not everyone who passes goes straight away, and as far as i'm aware Sandhurst is down numbers. May intake (banker and stoner intake) never really fills up and normally has one company with only two platoons in it.
If you get the pass at main board they won't kick you out for being a few months north of the 26 mark.
As for your boots, don't worry its not going to count against you and the reason they say you need boots is to stop horribe civvie types from claiming when there trainers offer no ankle protection and they break them. Worst case you don't get to do the assault course, not a big deal and not worth paying £100 for a pair of boots for 15 mins on a visit.
I've recently attended a FAM visit for R Signals. Most people were loaned a pair of boots for use. My pair looked and felt as though they had been in the system since the 60's, but they sufficed (arguably the reality of the army!).
Ex Full Spectrum is a brief around the FOB (forward operating base) built at Blandford for training purposes showing what they get up to.
CS95 is the combat uniform currently being phased out to make way for MTP (which google could have answered)
Edit: am only on my phone. I might answer your other questions when I get home. PM me if your on the Signals visit and I can try to answer your questions or concerns.
As far as your entry to sandhurst goes, your pushing it for time imo. As above, I believe you have to be at RMAS before your 26th birthday? If you havn't done so already i would have a chat with your ACA and discuss the finer details, as they will have your back story and may know about the medical problems so should be best suited to advise.
To answer your question of 'what level will the staff taking the day and the soldiers we interact with expect us to be at'. They will really have little expectations, however they will expect you to have a fair fitness level. As per the programme that you would have been sent, you'll see that there is a PT session at about 0630 the second day. This is partly to assess how motivated and determined you are to get on after a good night in the mess (we had drinking games with space hoppers etc until 2am), plus a bit of phys in the morning is always a good thing. There is also a few runs of the assault course which can hurt if you had a heavy night (like i did!). Just suck it up and push through.
There is an element of assessment that the staff will carry out, and this is to assess suitability for Sponsorship from the Royal Signals. Sponsorship is non-binding, and is not the same as confirmed cadet status. However, it is a good indicator that you've given a good account of yourself and that your going in the right direction. It's also a boost for the confidence when/if you get your letter through the door. I didn't know that the visit was assessed for sponsorship until the final brief 5 minutes before I left, so was pleased when the letter came in a few days later. As i understand it, the visits are not reported to the AOSB/RMAS staff, but happy to be corrected.
My advice is to just relax and enjoy your time, and realise that you are there to learn about the Royal Signals. The first day is mostly briefings so pay attention to the staff and if you've got a question, put your paw in the air and just ask. I was the annoying bloke who kept asking the questions, but there were others (as a few of them told me after) who wanted to ask but didn't have the bottle or thought it was a stupid question. The staff want you to ask questions. It shows your paying attention and are interested in what they are talking about.
You won't be given CS95's anyway. You'll be issued coveralls and a coloured/numbered bib much like AOSB.
Hope this helps, and remember to relax and be yourself