Jim, if you use rebar to connect the individual pours, you'll want to have the rebar in the first pour extending at least 24" out beyond the first pour, as Tom mentions doing. Repeat this step for each pour, tying the new rebar section to the pins extending from the first. Use rebar chairs in the centers of the pours to keep the bar from lying on the ground & not embedded in the slab.
Personally, I'd use the 4" square wire mesh (along with the fiber mesh mix), and not the rebar. To do this, on the side you'll be extending later, cut your form board in half lengthwise, lay the wire mesh down over the bottom half of the form board, then screw the top half of the form to the bottm, pinching the wire mesh between them. You can leave the balance of the needed length of wire mesh rolled up, or cut it where you have 24" or so extending beyond the first form, as with the rebar.
You wont need to use expansion joints between the pours; this would instead normally call for a control joint. You automatically have this, because you are creating a "cold joint" by pouring against a previously cured slab. You do need to cut control joints in the other direction within the pour, too; I'd suggest every 8' to 10'. Continue these with each new pour, or have them done with a concrete saw after the entire job is completed.
You DO want an expansion joint at the joint to the garage & rebar pins at the joint to the garage if you live in an area subject to soil movement or hot/cold weather extremes. You'll need to drill into the garage slab 3" to 4" and use 16" or 18" long rebar pins to ensure the new slabs do not begin sagging at the garage entrance.