They are a bitch. Everyone has their own theory on what order to complete them, it really depends on you, but if you are working at the same time, it will be full on within the 2 year window.
Really depends on how you work/study. The "easier" subjects are Law, Human Factors and Meteorology, Systems is mostly wrote-learning, so long as you understand the background concepts, then the "harder" subjects are Performance & Loading, Nav and Flight Planning. Flight planning is a prick of an exam - I would highly recommend doing the in person course at AFT at least for flight planning. Also worth doing practice exams from multiple sources (Avery, AFT, ATC, etc) to cover off all of the exam question styles.
Whatever you do, don't leave flight planning to the end. Alot of people try and knock that off first (but then you run the risk of losing it if you time out).