I'd love to. For volunteering, care home is the best place especially for under-18s. For WEx, whenever you go see a Dr, show your interest in medicine and that you are a really capable student and then ask if you could shadow them (for me it was my GP). Don't be disheartened for not finding WEx - I got rejected about 10 times over the span of 3 months before securing my first and only placement. Also, there are some free online WExs (one which I def recommend is the BSMS Virtual Work Experience but other good ones are there as well). Plus, you should do wider reading (reading medicine books) on either the medical experience, a good one being When breath becomes air, or you can be more specific and read in-depth about a medical topic which you like (I'm reading a book on the mechanisms on the heart). This may seem a lot but just do a few hrs every week consistently, u barely notice it and it slowly adds up to be a lot.
Now, about the UCAT, it is quite hard, but in a way its proportional to your hard work - the more hard work you do the better your results. It consists of 4 sections - VR (english), DM (logical reasoning), QR (maths), and SJT (judgement). Some YouTube videos explain the structure of UCAT quite well so I'd recommend watching those.
Its best to focus on this after your Year 12 finals, and maybe even when the summer starts. You can book this anytime during summer. For preparation, you would need abt 150-180 hrs to consistently get 95th percentile +, but you can divide that among 7-8 weeks by studying 2-3 hrs, and ramping it up to 4 hrs when the exam date is closer.
Now obv you need to do a lot of practice so the free official UCAT Q bank won't be enough so you should get either Medify or MedEntry (I used MedEntry and I highly recommend it). The strategy for preparing is to do a full mock, identify your weak areas and work on those one by one (I focused on VR for the first 2 weeks then moved on to DM and worked on that for 2 weeks). Keep in mind that you should not spend equal tiem preparing for each but rather spend more time on your weak areas and less time on your strengths (I barely did the QR but my UCAT practice was heavily VR-focused).
This is basically an overview and you don't need to worry about the specifics until the end of Year 12.
Last thing, Further maths is good but you should only do it if you love maths. And with all honesty, its better to do an EPQ rather than Further maths for medicine - its much more useful and showcases key soft skills which may otherwise be hard to evidence.