1. The short answer is no, not really. The long answer is form rules are meant to respond to web events during a client interaction with the form. The only way a workflow can really interact with a form is to make one available to launch by triggering a client event either via a generic Client Event or a Smartform Client Event. That still requires a user to go to their worklist and open the worklist item to launch the form, or click on a link in an event email to launch the form. Workflows cannot force rules to run on forms that are open and being interacted with by a user.

2. https://help.k2.com/onlinehelp/k2blackpearl/UserGuide/4.7/default.htm#Thick_Client_Wizards/For_Each_Thick_Images/For_Each_Event_Wizard.htm%3FTocPath%3DCreate%7CK2%2520Studio%7CWorkflow%7CEvent%2520Wizards%7C_____6 is the relevant documentation on 'For Each' in Workflows. When you say dynamically assign the item collection, do you mean have a datafield as the Source of the 'For Each' so that its type is determined at run-time? If so, I don't think that's possible. 'Item References' are created at design time for individual items in the loop and it needs to know what the type is at that time. There are very limited instances where you can use datafields at design time for event sources (IPC Event is the only one that I can think of off the top of my head) and those events make you first pick a concrete source (a Process path in the case of IPC Events) to get the design templates created, then let you switch to a run-time datafield.