304 is the standard kitchen grade.
The main difference between 304 and 316 is 316 has molybdenum added to it which gives it an acid resistance and so allows it to stand up to more nasty stuff.
If you'r looking to do cool little gifts like that, stainless countertops should be just fine, most likely they are 304, rarely will they be 316. You probably just want the corrosion resistance malleability of stainless for your ideas which it should offer.
Stainless welding is fairly easy, just be careful with cooking it, once stainless gets hot and molten, it tends to float some materials around which can prevent the oxide layer from building on the surface of stainless. This happens due to the chrome in it. Once metal has more than 18% chrome (Or something similar) it is considered to be "stainless" as the chrome will protect it.
I could go on for hours, I am trying to stay on track.
BUT! Most importantly, make sure you leave the torch with its postflow over the weld once your weld is done, give it a good 5-10 second post flow to allow the weld to cool with a shield over it and then your good to go, by removing it too fast you can contaminate it and once again, prevent the oxide layer from rebuilding.
By the way, that oxide layer rebuilds naturally once the chrome surface is in contact with oxygen that's why there is such a stress on not contaminating stainless, dedicated brushes, grinding wheels, etc.
Sounds like a great idea though, I think they will be happy. Are you planning on painting any of this stuff? Stainless is very good at getting discoloured after welding which ruins the aesthetics but there are ways to handle it, just depends how far you want to go.
There, I feel better now that I got to babble