with 4.0, the newly added Operation Behaviors
    Read-Only Attributes For Type and State and
    Read-Only Attributes For Condition

for an earlier version you can use the workaround based on read-only presentations
   https://jazz.net/library/article/808/

hope it helps.

Requirement such as : say you have createdby to be set in created state and transition to request for build, createdby should be read-only can be addressed. 

i am sorry but I dint understand the part where you say "the mandatory fields that i want to fill in state2 are getting missed out" - the mandatory fields in State2 will show up once you enter that state.  so if you want say buildduedate to be filled in State2, you can use Operation Advisor -> Required Attributes and set buildduedate as required in State2.  This will stop you from going to State3 unless value for buildduedate is filled in State2

To what I understand, transitions start after the desired action is chosen and saved.  Only when you enter that state, the corresponding features will show up.  The behavior you see with Read-Only is same you would see with Required Attributes and same as any other State based activities. 

If  you are looking for a dynamic change in the presentation elements based on the state transition action chosen, at the moment I dont see any functionality that can help you with this.  This will be difficult as well since you can have multiple actions leading to different states from one given state. 

However, if you need something to be checked before a transition happens, you can use Validators.