I just made a Heffeweizen for our brew club Oktoberfest party next weekend. I didn't want too much banana aroma or flavor, so I did a ferulic acid rest at 42 C for about 20 mins along with a decoction to bring it up to 64 C for the main mash, then another decoction to bring it to 76 C for a mash out. Ferulic acid is the precursor to the clove phenol that the yeast will produce. I wouldn't muck around with 2 decoctions, especially if you haven't done one before. If you want to do one, just do it for mash out. Or, you could just do a single infusion at 64-ish.
Basic recipe would be 50% wheat and 50% Pilsner. Make sure you boil for 90 mins. I added Tettnang hops at 60 mins and 20 mins left in the boil, then fermented at 19.5 C for 10 days. It has a more pronounced clove aroma and flavor than banana, but there is still a little banana. Nicely balanced, I think.
I used White Labs WLP300 for mine, but Wyeast WY3068 (Weihenstephan strain) would work the same way. I think they are actually the same yeast strain.
Cheers!