How should I invest $250,000?

If I continue to save and my investments keep doing well, I should have saved $250,000 in the next five years. I will be 30 years old by then. What would be the best way to invest that amount if I want to put a portion of that towards a mortgage and invest the rest in an index fund, ETF, etc? Also, what's the rule of thumb for a mortgage? Is it better to pay cash or get a mortgage, and why? Dave Ramsey says to pay cash but other financial professionals say to get a mortgage, so I'm not sure who is right.

Also, what would currently be the best way to deal with my student loans: the balance is currently about $10,000. I'm contributing $3,000 towards my 401k and $2,000 towards my Roth IRA. Should I stop contributing to my 401k and IRA accounts and focus on paying off my student loans first?

Thanks

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