How should we get legal help?

We have some investors who are interested in helping us in our seed round. For that and probably a lot of other issues that will come up in the near future we will need someone to take care of the legal side of things. We were wondering if--for a startup--it's best to have a) a partner of the company with a legal background, b) hire a lawyer as a regular staff member, or c) just always get legal help externally. Option c seems to be what most startups are doing, but then there seems to be so much legal work at some point, wouldn't it be more cost effective to have an in-house lawyer from the start? I would be grateful for some advice based on your professional experience, thank you!