Prawnmee, yes definitely if your cycle is not regular, then you should BD over a longer period of time.
As for tracking O day, I guess it depends on your personality lor. For me, I find it less stressful if I know what is happening, I rather know than keep wondering and wondering when is AF due, when is O day, did I BD on the right day, etc. Also, I want to make sure that there are no health problems that can affect ttc. And most importantly I track my O day because DH and I don't BD very often, so I don't waste my chances if possible.
Actually the first cycle that I chart BBT, I was quite stressed, until my cycle ended up 45 days. haha. But after that, no probs, no stress.
If you're the type who is quite relaxed, still quite young, and can slowly try for 6 months or a year, then tracking your O day is not so important. Just relax and BD when you feel like it. Most gynaes won't tell you to track this and do that and they won't explain to you about all the details about LP and all that. That's because sometimes it can add stress and affect ttc. Most gynaes just tell you to BD more and just want you to relax and if cannot conceive within 6 months (or a year if you're young) then only they will see if there is anything you need to change or do.