Hi MrsB I'm not really an expert
I have just suffered more than my fair share of fertility problems and have tried to read my way out of them
Seems to be working! I am doing well thanks for asking, I have been diagnosed and treated for Ashermans Syndrome I now have normal cycles and have just started TTC.. watch this space 
Your questions:
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It is supposed to improve quality of EGCM and regulate cycles. The only "sciency" information I have ever found is a study that proved that it is "useful" for treating PMS. I dont think there is any other medical evidence that it is good for TTC, but anecdotally there is lots of positive stories. I used it for a few months, didnt notice much difference in EGCM, but my skin and hair look amazing
(I tried grapefruit juice for only 3 days and noticed a massive difference) You shouldnt take EPO after ovulation as it apparently causes uterine contractions and therefore can impede implantation.
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Short answer - on the day of positive and keep going.
Long answer - I love ov sticks, but you should be skeptical of what they tell you. The instructions say you will ov 12-36 hours after the positive, but it could be even longer. Stress/illness/travel can delay ovulation, or cause it not to happen at all. Also if you have PCOS you may see positives all the time but not be ovulating. The OV stick detects the surge of Lutenising Hormone which is the messenger from your brain to your ovaries which says "ovulate now!" Just because you detect the message it doesnt mean that you definitely WILL ovulate or that it will happen within a set time. (sometimes the ovaries arent ready and will ignore the message) So dont stop SWI too soon. I dont stop SWI until I have detected a temp rise or feel that my cervix has changed back to non fertile position.
Also, sperm need several hours to be ready to fertilise an egg (they undergo a process called capacitation once in the uterus) so its always best to have the swimmers in there ready waiting on the egg not the other way around. That means you should SWI as soon as you see the positive (or have done it the day before) in case the egg pops out exactly 12 hours later
- There is a lot to be said for throwing the tests out the window and just having sex often and when you feel like it. Its certainly better for your relationship. I also believe that your body subconciously tells you when you are ovulating too, I am sure the times when I feel more randy are when I am ovulating. (thats how DS was conceived, he was a happy accident
) The other advantage to sex being "natural" as opposed to "programmed" is that you are probably giving DH's sperm the right amount of time to be "restocked". Doing it too often (especially if DH is older or has low sperm count) can result in lower quality sperm. Also doing it too often can result in you both getting knackered and not being able to continue so you only ever do it at the beginning of your cycle and then give up!
BUT if you do want to try and program it all you can input your SWI and OPK data in www.fertilityfriend.com and it will give you a score
so you know if you timing is good or not each month. Its a bit demoralising when you get a "low" score though.
Not sure what you would have scored this New Year as (if i understand right) you didnt get a positive on the OPK (just one feint line and the control line)? If so, then we dont know when the real LH surge was so its hard to say when you may have ovulated after that.
Very best of luck! (and thanks for the ego stroke 
googlewhacker I too would like to go back to those days when I thought I would get pregnant just by brushing up against a penis. Oh how things have changed !