Not sure how much yeast nutrient you should add, but I'm guessing that there are some recommendations on the container somewhere. As for the yeast, you should be good with a starter. If you have some time before you're planning to brew you could also step the starter up to 1L.
I've used yeast over a year old a few times and I've found that as long as I do a starter and step it up once or twice to increase the cell count, it works just fine.
Hope this helps.