CBay - you are stressing too much about this.
Firstly - Get rid of the OPK's immediately, they are not going to help you. If you wait for the OPK to be positive before DTD then you are leaving it too late. If you insist on using OPK's then use the sperm meets egg plan This will maximise your chances of concieving. (But does lead to sex being a task rather than helping your relationship.)
Everything Frankelly says is true, and I agree that the most important thing is that you and your partner have a healthy lifestyle and are having regular sex.
Next - regarding risk of miscarriage, you don't even know if you have a short luteal phase, let alone if it will cause problems. Only very short luteal phases of less than 10 days generally have any problems.
You say monitoring your cm you think you ovulate around day 14, and your cycle is approximately 28 days - that is text book perfect. Definitely NOT short luteal phase.
Cycle length of 27 to 30 days as you have is normal.
CM is a good way of monitoring fertility, though it is quite hard to do accurately, especially trying to distinguish between EWCM and ejactulate. If you see good lubricative CM, especially EWCM, then that is a good time for DTD.
Delayed ovulation does NOT reduce your luteal phase. Your luteal phase is a fixed length of time. The time before ovulation can vary due to illness, stress etc.
I am not surprised to hear that your ovulation is late this month considering how much you are stressing about ttc. If you ovulate today on day 20 and your LP is 14 days then your period will arrive late this month at around day 34. Don't go doing pregnancy testing early, it is expensive and will only stress you more.
Please do not stress about miscarriage before you have even concieved. I have had 12 miscarriages (and three wonderful healthy children). Miscarriage risk is decreased by reducing stress - so again I repeat relax. You cannot go having hundreds of tests to see if you can prevent miscarriage before you have even concieved. Even with all the tests, there is little that can be done to prevent miscarriage if it is going to occur. (short luteal phase is not something that you could easily change anyway, but you don't need to worry about that as you don't have it!)
Focus on making sure you and you partner are as healthy as can be and focus on keeping your relationship strong.
You say you "want to conceive but equally I don't want to increase the risks of MC. ", if you want to 100% guarentee no miscarriage - then don't have sex and don't concieve. Miscarriage is very common, many women miscarry before they even know they are pregnant. It is not something to be fearful of. If it is going to happen it will happen.
So if you want a baby, and your cm is now fertile and you opk is positive then dtd. You only have a 20% chance of concieving each month. You will have left it a little late for concieving this month already by waiting for a positive opk, but hey it only takes one sperm right!