Well, it looks like the big limit on seemings is that you can only use it on yourself, things that belong to you, and people you have some degree of mystical hold on (or who have some hold on you - promises work both ways.)
Other than that it's pretty wide open, though as a GM I'd probably add further restrictions - for example, making illusions you put on others fade at dawn, or not allowing you to make a band of 50 mercenaries you hired look like oni; in general, I'd say the maximum mass limits for veils would apply here. But those are house rules; use or not as you see fit.
This also means that you can't use seemings to make nothing look like something; there *has* to be a core item or person there for you to modify.
So, no using seemings to make illusory monsters out of nothing. But you could use it to make your partner look just like that guard you knocked out and dragged off into the forest...
As for what senses it can include - I would actually say it *can* include touch - somewhat. You can make silk feel like sharkskin (or vice versa, though people would get to realize something was off when the silk 'bit' them...); what you cannot do with mere glamours is create force where there was none. So if you disguise yourself to look like an ancient samurai, complete with armor and sword, it'll all seem real enough (as long as you've got some physical item to form a core for the "sword" - perhaps a stick you picked up in the woods) - until you get into combat, where the "armor" will provide no protection, and the "sword" will be of no more use than a basic club.
Of further note is that, if someone beats your discipline/deceit roll to establish the glamour, they get to know that there's something off about it - but they don't actually get to see through it. People who are used to D&D in particular should note this difference. So if you're a shapeshifter using glamours to conceal the fact that you just shifted back and haven't found clothes yet, and someone beats your discipline/deceit roll, they don't suddenly see you naked; they just get to know that, for example, the shadows on your clothing don't match the light sources around you.