I would say its only worth keeping one months worth of outgoings in your current account regardless of income. As you say the rest can sit in Marcus at 1.45% which can be classed as emergency fund. I’d build that up to cover a few months of outgoings and add to the house deposit to get a better LTV then get cracking at the personal debt as its a decent low %.
I’d only go looking at investing/pensions once you have no debts and emergency fund built up. You need to be able to be happy with whatever you invest in also losing. If you want to dabble theres Freetrade that can help you get into it, create a S&S ISA, go with ETFs and look for a five-ten year return min. Picking individual companies is a bit more of a gamble, but if as long as its not all eggs in one basket it should help average out the return.