I agree with others that you need to learn bicycle mechanics better, but I also recognize that some people do not have a good aptitude for that. I suspect you are one of the later. A good book on bicycle mechanics may help. I can't recommend a book, I have none, and if I did recommend one it would be in english. If you do not have a good aptitude for mechanical things, there is nothing I can suggest to improve that.

If you do not have a chain catcher, consider getting one. You never explained well what your downshift problem was. If you were dropping the chain, the chain catcher is intended to prevent that. They are cheap and can prevent a lot of frustration.

I think you should consider a new crankset, 110/74mm. Your 24t 74mm chainring would still work. You would have to decide what size chainrings you want for the middle and outer positions.

If you get a new crankset, a new bottom bracket may be appropriate if spindle length or method of connecting the cranks is different. I you get a new bottom bracket, you will have a lot of additional questions about which one to get.

Eight speed versus nine speed cassette, I am perfectly happy with the eight speed 11/32 that I have on three different bikes. I can't speak about Shimano cassettes, mine are all Sram. But when I built up my first touring bike almost 10 years ago, I was trying to decide which to buy, the eight or nine speed. The Sram eight has 11, 12, 14, 16, 18, 21, 26, and 32t cogs. The Sram nine has 11, 12, 14, 16, 18, 21, 24, 28, and 32t cogs. The only difference is that the eight has a 26 and the nine instead has a 24 and 28. I concluded that I would be perfectly happy with a 26 instead of the 24 and 28, thus I chose to go with an eight speed. Since then I have been happy with my choice.

I think I would be perfectly happy with your gearing, but you are obviously not. So, you need to decide what you want and get it.