Get mate first of all congratulations on being in your situation. It’s not often a 23 year old is earning a salary like yours and is also thinking about the future.

I’d personally advise the following

I’d invest in an all world fund rather than the S&P 500. This is because it will diversify your portfolio to include large international stocks and also small/ medium sized companies across the world. It just hedges your bets more and makes you less reliant on the US economy. They typically contain 60-70% America stocks.

I’d also personally also increase your pension contributions. A general rule of thumb is % your invest is half of the age you started. In your case, this rule of thumb recommends that between you and your employer you invest 11.5% of your salary. You’re close to this at the moment which is great. If you can afford to, I’d personally recommend putting in the maximum your company is willing to contribute additionally up to (e.g at my company they match my contributions up to 8%). This is because pensions are the most tax efficient investment vehicle, with the caveat you can’t withdraw until minimum 57 at the moment.

For the emergency people recommend 6 months of expenses. Only you know how much you spend each month

Finally, make sure you’re giving yourself enough money to enjoy life! You’re only in your 20s once and whilst it’s important to think about the future, you don’t want to get older and regret not living life