I don't understand your first question, about patterning parts in a sketch. You can pattern features or bodies in a Part file, and you can pattern components in an Assembly. You can pattern sketch entities within a sketch, but I don't recommend it, and it doesn't sound like that's what you need anyway. Can you please explain further?
For your second question, see #10 here: Frequently Asked Forum Questions .
So did my answer help, or do you still have questions?
It would be easier to advise you if you posted a screen capture of your assembly, but if I'm picturing it correctly, you shouldn't use component patterns for this project.
The reason is that component patterns don't support dynamics in mates. Pattern instances always move and rotate in the the same direction and orientation as the pattern seed. If you're making a pentagraph, this might seem like what you want, but even in that case, you shouldn't use patterns because you then have no flexibility to resize or re-imagine the components.
The best way to construct this kind of assembly is insert and mate individual instances of the parts. If the assembly legs or or shelves contain hardware or mounting brackets, then I suggest making those into sub assemblies and instance those to reduce the number of components you have to mate.
To address your second issue: the first component you insert into an assembly is, by default, fixed in place. It won't move when dragged or acted on by mates. You can fix components manuall and they're indicated with an (f) before the name of the component in the feature manager.
You can remove the fixed status from a component by right-clicking on it in the assembly tree and selecting Float and then choosing which configurations from which you want to remove the fixed cosntraint.
It's advisable to have one component in the assembly fixed at the origin as it is easier to make use of the origin and assembly planes.
I suggest you do again the tutorials on creating assemblies and mating components.