Read the posts on the link below and it will answer your questions.

Here is a link that might be useful: Growing Vinca

Depends on the mulch you will be using...I use pine fines....and they root well between the mulch bits.
Once it establishes it's there for good!...I have been ripping it out of one spot for years....wish I could give it to you.
Linda C

I'm trying to do the same, and I was told by several nursery people that mulch was a bad idea, because it inhibits its spreading by surface runners. So I raked up the mulch (carefully), and put down a thin layer of compost, and I water regularly and use Miracle Gro liquid about once a week. So we'll see.

Any feedback on my method is welcome.