Now that you have your guide shape you can start arranging the elements of your pattern. At this point you may want to turn off snap to grid and turn on snap to point by going to View>Snap To Point. This will help you with aligning your elements to the sides of the guide shape. Feel free to play around with the scale of your objects now, to make sure they fit.
One thing you will need to be careful of while you’re arranging your elements is their position in the layers. You may need to send objects forward or backward to make sure the part of the element you want to be visible is on top. This can get fiddly and confusing, so make sure you name your layers meaningfully.
Once you have arranged all the elements into the guide shape and you’re happy with the graphic you can get onto the next step – tiling. First, I’d recommend saving the document you’re working on and opening up a new one. Once you have a new document, copy your graphic in it.
At this stage I’d like to scale my graphic down, so to ensure the paths stay to scale, select all (Command/ Ctrl+a) and go to Object>Path>Outline Stroke. This will turn any stroke into a fill. Alternatively, if you’d like to keep your strokes go to File>Preferences>General>Scale Strokes & Effect. This will keep the scale of the stroke width consistent even if you re-size.