I’d talk with those who you’re thinking about starting a company with.
Usually there is a contract signed between the employee and employee about things regarding “conflicts of interest”. These are usually setup so you aren’t working “for the competition” or “working some other job that prevents you from completing this one”. As no company wants to pay you if you’re working for someone else, or directly working against the current one.
Since you’re creating your own company, you can set your own rules in that regard. I’m not sure if there are any overarching legal rules imposed by governments in these situations, it’s usually a company-employee contract that is the “legal binding”.
So if you plan on freelancing on the side and helping this company start, I’d talk with them about it, so it can be figured out to allow each party to get what you want.
It’s not directly clear if this is a good idea or not. It really depends on how you plan on balancing your 2 workloads, and if one impedes on another. If your a freelancing, it should be a given that you take jobs on that you can accomplish within the timelineyou provide. If the timeline doesn’t work out, you don’t take on that job.
However, from the company side, if there is an increased workload that impedes on your freelancing, you have a tougher decision.
Ultimately, you need to decide how much work you can ultimately take on from the company, and leave some extra time that isn’t included in either so you can be flexible. The last thing you want is to be overloaded on both fronts and not be able to deliver in either.
Finally, there is also the question of payment. Freelancing costs range depending on what your able to do and find. Where-as starting your own company can costs money, along with time and effort up front, so I’d see it as an investment. This is of course if your an owner/founder. If your just another worker/asset its similar to your own gig.
Good luck, keep learning keep building 