Well it depends on you. However larger sigils require more alchemic output and since we are restricted to a level 3 I think a 5 to 10 foot sigil should be the max. 

A pre crafted sigil is like you have a sigil drawn on a piece of paper and that paper tucked in your shirt for later use. 

Well we will basically just follow the order presented, go with the flow of the RP. It will be divided so the others can work on the other part and a final touch will be made to merge it together. xD