What exactly is it that you're worried about Chitter? Is it that you're worried you won't be able to do the fertility treatment with the best possible mindset? I don't know what kind of wedding planning you're doing, but I really can't see how a wedding two years down the line will get in the way of treatment now. If you've reached the top of the waiting list and meet the BMI criteria, then you're likely to be doing treatment in the months ahead - possibly even before Christmas (depending on your protocol).
Do you really have THAT much wedding planning to do in the coming months? I had a relatively big wedding (100+guests) and we did all the arrangements in the 6 months before the wedding. Of course everyone's different, and if you're going for all the trimmings then there will certainly be more to organise, but I'm not sure how much you'd do 2 years in advance apart from book a venue and send out a "save the date".
Depending on your protocol, one round of IVF/ICSI takes no longer than 2 months. If you do two rounds, that's unlikely to take you past the spring. I'm in the middle of my first cycle now, and I certainly wouldn't want a wedding to be planning in the weeks ahead, but further ahead would seem perfectly doable.
Of course you shouldn't rush into anything if you're not ready, and IVF/ICSI can certainly be all-consuming. But I also agree with 18years - delaying for two years could have an impact on your chance of success.
Would it help to maybe understand a bit more exactly what the treatment will involve? And maybe also think about what actual planning you'll need to do for the wedding? There are some great resources for both online - including a "wedding countdown" that tells you all the things you should be doing 1 year, 6months, etc before the wedding (I was WAY behind on all those things, but it was still an amazing day!).
And of course feel free to ask more Qs on here, there is an incredible pool of knowledge among MNers!