You can have as many teammates as can legally fit in your vehicle. The final deadline for registering your team mates is in June but the earlier the better for getting their rally swag, access to the team only Facebook group etc
If none of your friends are adventurous enough to join you, look on the Find a Teammate group and see who else is in the same boat - there are always a few others looking to corral some like minded types into an adventure.
Alternatively you could do the Rally on your own- you will meet people along the way. You could go by motorbike- it's harder, but cheaper and you are bound to meet people.