There is only one method of computing the WACC. You need to calculate the cost of each source of finance independently and then take a weighted average, weighting by the total market value of each source.
With regard to using forward rates and money market hedging, it is impossible for me to explain in a few lines here. However there are full lectures on this website which you can watch.
(And lectures also on calculating the WACC).
If you have specific problems after watching the lectures then please do ask.