As I think someone else mentioned having a 9 speed transmission on my Haibike means that replacing worn out bits is much more reasonable than systems with more gears.
Back before this inflation malarkey when I was commuting regularly a 24 mile round trip to work and back, 14 mostly off road to work and 10 back on the road, I had bought a job lot of the cassettes I used in 2019 when I noticed they were cheap, Shimano HG400 9 speed, 12/36, for £12.50 each delivered, stacked on my garage shelf. I still have one left!
Chains were also cheap, I looked for deals and remember buying two delivered for about £7.
The only thing that cost more was the Narrow Wide chain ring as I initially bought quite an expensive one, and liked it so much I have kept buying them. They last around 3,000 miles but cost around £50, ouch.
So looking back I was sadly a bit profligate when I was commuting, not bothering to measure chain wear and just bunging a new chain and cassette on when my top gear (It was always my top gear) started to jump under load. But hey it was costing less than £20 to do that back then (2019 not that long ago).
Now even 9 speed parts have gone up, £25 for my cassette and over £15 for a chain.
So maybe I will try a new approach to see how it goes. The three chain approach.
With a new transmission start with a new chain, chain 1. When that reaches the .5 point, take it off, clean it and store it and put a new chain on, chain 2. Do the same with chain two at the .5 wear point and put on chain 3. When chain 3 reaches the .5 wear point put chain 1 back on and run it to the .75 wear point. Take it off clean it and store. Do the same with chains 2 and 3. Then put chain one back on and repeat the process every 200 miles and see how long your transmission lasts. Can I be bothered, I am not sure!
Regarding mudguards, I have tried to get as much mud coverage as possible. Cable ties are your friend!