High earning can be a trap when looking for more from life as it is not the same as wealth. Lifestyle inflation can keep you living pay-cheque to pay-cheque if you're not careful (bigger house = bigger mortgage, bigger bills), holidays, debt, "keeping up with the Joneses". In addition, the earnings come with more responsibility, expectations and results, meaning less flexibility and more on call. Now some lower paid roles fall into the pressure trap too, and you have to work out if it's worth it for that salary.
Your best bet is to invest money through a S&S ISA. The earlier you do this the sooner you start benefitting from compound interest. Average growth of the world index funds is 8-10%, inflation adjusted is 5-7%. You just have to be prepared to invest for the long term to see the benefit.
The second thing is to live debt-free. The sooner you are free of mortgage and other debts, the sooner you have more choice in when and how you earn. This is a major trap for high earners, yes you can borrow 500k+ and afford larger houses or more expensive areas, but then you HAVE to keep earning to pay the mortgage. The counter to this is to just "off set" the debt, e.g. invest the money to grow, and know you could liquidate to fund mortgage payments if push came to shove. I prefer this approach, so that my assets are more liquid and therefore more flexible, rather than tied up in my primary home.
Your most lucrative option is for you and your partner to invest in growing his business as much as possible, but it is high risk. If you want to look to a future where you're doing housing development work to grow wealth, then look for opportunity for his business to build credentials in this space.
Home renovation is not as lucrative as it once was. It is all about location and what work needs to be done. The cost of materials alone is taking much of the profitability out of renovating and there is even lower cost associated to knocking down and rebuilding in a growing number of cases. And that could be the route to take, buy plots of land with derelict homes or blank plots with planning, live in a temporary caravan or camper on the land and build. You have the benefit of residential land being less than the SDLT threshold, if you have 25% LTV for the mortgage required, you can access self-build mortgages. When you're building you don't need to pay VAT, where as renovating a habitable home does incur VAT (make that make sense, since we should be enabling upgrade of housing stock)