I doubt anyone starts off buying and flipping houses with salary money these days sadly. You would need ...
an inheritance lump sum
a development loan, if you can prove you have skills in the housing renovation business
or to live in the house itself and do it up as you go, risky as it might not yield what you need, and you might not want to or be able to live in the place that would yield biggest returns. A family from Guildford who own a 3 bed can't relocate to a HMO in Leeds they are doing up as 5 individual student flats, even though that is probably where the money would be.
The thing is, all the tax and wealth stuff is carefully fixed now, there's no loopholes, we aren't in the 90s. Your capital makes about 4% at most wherever you put it, and the less capital you have, the bigger the interest on any loan as the bigger risk you are.
If your capital is your house- by the time you move and pay stamp duty, you either make nothing or under 4%. If you rent and then buy to let and do up, then the other taxes ensure you make less than 4%. If you sell your house and put it all in bonds, stocks, shares.... and rent....guess what the market makes just under 4% on average.
Once you're maxing out a pension there is little you can do but pay off the mortgage ASAP, work as hard as you can, insure yourselves against ill health (its own kind of racket).
Your husband's business is another matter- there are indeed ways to scale up successful businesses but it needs a lot of different information about what to do in the specific market you are in. And skilled behaviours, it's important to recognise what you yourselves have skills in and where you need to buy them in (for example a great electrician may be less good at admin and marketing). Growth is a process where you have to look at where the bottlenecks would be (the electrician gets some great marketing then can't handle the increased business it generates) and plan for different stages of the business.