When you switch bank there’s no need to close your old account. Just keep it open so that you can make the odd cash deposit and transfer the funds to Monzo.
Cash deposits are a drawback of having a Monzo account, you need to weigh up how much they matter to you and whether keeping your old account would be enough to allow you to open a Monzo account alongside it.
I ride a motorbike too and don’t swap them out that frequent. If that’s your thing though it’s cool
For me I always keep my cars and motorbikes for 2 or 3 years before swapping as that’s usually the length of the loan on them. I’ve found this is a good length of time to really enjoy and get some good use out of them before moving on, upgrading and trying something different.