There are two types of solid structures that aren't made of simple repeating units: glasses and quasicrystals.
When a crystal forms from a melt it requires the atoms/molecules in the melt to reoganise into the crystal structure. If the rate of solidification is fast enough the atoms/molecules don't have the time to reorganise and the solid formed is effectively a solid liquid with no long range order. The best known such material is glass, as used in windows, but many different amorphous solids are known. Ice can form an amorphous solid, though rather extreme cooling is required.
A quasicrystal is a solid that looks locally crystalline, but has no long range order so it can't simply be built from repeating units. In my days working in this area no examples of quasicrystals were known, though I note the Wikipedia article reports that real life quasicrystals have now been observed.
Your questions 2 & 3 are really part of the same question. Water forms many different types of crystal structure. Different structures are stable under different conditions i.e. different ranges of temperature and pressure. Under normal conditions ice always forms the structure known as Ice 1$_\text{h}$.
It isn't clear whether your question 3 is asking only how many different forms of ice there are (in which case see above) or whether you're asking more generally how many different types of crystal structures can exist. There are ony a finite number of possible crystal structures - in fact there are 230 possible structures. These are known as the crystal space groups. All crystals can be assigned to one of these groups.