I have seen people have that spacebar problem before. I don’t know if it’s a browser thing, if you just need to clear the cache or use a different browser. But no, it’s not a setting or anything, at least that I’m aware of.
Yes you can have linked objects use different materials. By default the link in the material is set to Data, meaning if you change the material in one, all the other objects that are sharing the data will get the same material. But the link feature in the material can be changed to Object, which will allow you to set a different material per object will they remain linked.
