Are there any group queue restrictions in competitive?

For Overwatch Competitive Play, as of Season 2:

• For Bronze through Diamond ranks players must have a skill rating within 1000
• For Master and Grandmaster ranks players must have a skill rating within 500

Ranking groups are provided in the chart below

Yes.

In order to queue with friends, there are certain criteria:

• You must be at least level 25.

• Your account must not be banned.

• You must be within 50 Skill Rating of your friends. Skill Rating is a 100 point scale, and your initial rating is determined by 10 Placement matches at the beginning of each season.

Source