Our company is about to acquire a source code of a huge product.
What are thing to take into consideration when the handover starts, to make sure we have everything and be capable to maintain that product in the future?
The things you should make sure are :
Everything else is up to the current maintainer to hand over.
Firstly good luck.
Here are some of the things which you probably should ask for / be provided with.
That's about all I can think of at the moment.
You need to make sure that the team hands over the code will provide support for a period of time. Make it a signed contract!
You will have questions later on that you didn't know you had to ask upfront, so they need to "stick around" to explain stuff to you not just give the code, docs and whatever they have on the project.
When you have a project handover you loose one important thing: the original team experience.
You sometimes also get something you didn't expect: their hostility.
Is the company doing the handover getting a good deal with the handover? If they loose business because they turn the project to you, the (proud) developers that created the code might resent the fact that their "baby" is given away. You might get responses like: "It's in the docs you got" ... even if it isn't.
Technical aspects are good to cover, but also take into consideration the human side of it.
Does the code come with a test-suite? Do all the tests in the test-suite pass? How much coverage does the suite have?
I would recommend that, missing a test-suite, you make building the test-suite and related framework your first priority.