Hello Susan it's nice to see that you planning for your next exam before clearing the CPT.
Well it totally depends on you there is no bar that you should join the Articleship immediately after clearing the Group I but you can only be eligible for your final exams in the last six months of your Article Training. It's simple as long you will take to enroll yourself for article training more time it will take to enroll yourself for Final Examination.
And there is rumour in giving both the groups of IPCC together or one by one, however there is nothing specified by ICAI that a student should give both groups together or one by one.
Since if u are giving both the groups together u have an advantage to completely focus on your studies but if u are planning to give Group II in next attempt of Group I than u have to study for Group II with ur Articleship Training.