Good to know this. You are right. You have to first create FS item and then create a group account. This is the only way. But explain your users that they will hardly create group account so repeating it 2 times is not a big deal. You may think of creating Z program but it will be a modification to standard.
On your other issue - It seems you have marked object required for your CR. If you want to add multiple account, do not tick any option and ask users to add multiple account first. Save it and then click on each record and click on single processing. This will help them to create multiple GL accounts.
Another way out is ask them to fill up the GL acc no / COA first. Then when the request is submitted, assign it to the same person i.e your requestor itself so that they can fill up all the details.
Try any one it will work.
Kiran