I found spesh was at times difficult conceptually (eg imaginary/complex numbers) and quite different to methods. Although the content was hard, it's usually straightforward once you understand the concepts and have done some practice (methods had more 'trick' questions I found). I found spesh was certainly more work than methods but if you're considering doing something maths-related in the future (eg maths, engineering, physics and others) then it's a good subject to do, especially as the scaling is great! Try it out, it's a subject that was difficult and you had to put time in but rewarding and enabled me to do more at uni
Regarding your questions:
It can be hard to understand at times but that's why you have the teacher and time outside of class to go over things.
It has a reasonable amount of content but you're not overloaded with too much. I think it had more than methods but it wasn't a content-heavy subject, just the content covered took a while to learn
You need to memorise basic things (formulas) but spesh is more about applying than memorising - like many other maths subjects. And often if you think about things logically, the formulas will follow from that meaning you don't have to memorise the formulas as much
Methods is easier and more familiar content, while spesh is often entirely new content. There are new concepts and you have to wrap your head around imaginary numbers, vectors etc.
I think you could handle it
even if it's tough, give it a go. I didn't like spesh in year 11 (bad teacher), didn't mind it in year 12 (good teacher but I had some gaps in my knowledge) and now at uni I enjoy maths a lot (the subjects followed on from spesh). It's a subject definitely worth doing!