Ask HN: Do startups usually design their own site or outsource the work?

Definitely worthwhile to get a designer in, if only for the basic branding elements; logo, type, palette.

Spend some time on designer hangouts, like dribbble, find some designers you like and ask for some quotes. In my experience it's always better than what an 'amateur' comes up with and surprisingly affordable.

we currently do interaction design / wireframes ourselves and plan to get a visual/graphic designer onboard in the next weeks.

one point learned already here: a visual designer could have given valuable input early on. so try to gather some ideas from designers early on

Have you reached the MVP stage yet? I'm wondering whether it's viable to release before having a professionally made design.

no we havent released a MVP yet and i also think a mvp needs at least a "decent" design. (depending on your customers of course)

but we will do some user tests before the design is ready, just to find major flaws in the interaction & interface.

You could outsource the design part and write the code yourself?

Not really, Instagram was not.