Wow! You don't ask for much. hahahahahahaha
Simple answer to your simplest question....yes, workflow works with HCM P&F....in fact, it is the backbone of it. SAP provides standard tasks for the things you would think you need...edit form, approve form, save in background, read form field values, etc. Workflow also works in conjunction with CASE Management (SAP Records/Folders Mgmt) to actually store the "temporary" data all along the way (think of it as our "persistence" layer).
Now for your other questions...sorry, time for you to put in some work. You have a LOT to read and take in to learn/understand config and development for HCM P&F. It;'s a big Big BIG world out there. haha