Termites may cause a problem with rotted wood.

Where are you located?

If they'll tolerate your climate you could try cattails, swamp lilies, pitcher plants, and sundews.

i was so excited by hugelkultur I didn't think about termites... and now I just mulched a bed right next to the house! Now what?! As for the pond, I discovered that the gravel is actually 2 feet deep, as it was once a koi pond that must have been converted to a shallower one, That makes me think I need to put a liner on TOP of it before putting in my bog garden soil -- whatever that will be. Please keep your advice coming - you can see I need it on many fronts with this project.

The mulch around the house probably won't hurt anything if it doesn't contact any wood.

I think the leak is OK, because you don't necessarily want standing water for the bog. At the same time, you may even want more leaks or holes, to make sure the area is moist but not standing water (but different CPs will tolerate different water conditions so that's another thing you could decide about now, before fully committing to altering the pond liner)

I think you can use the log as part of the landscape/bog but not necessarily to replace the peat.

Now that your additional comment suggests the pond is actually deeper than you thought, how deep is it exactly? If the water is draining away, you might be OK with putting the growing medium on top of the gravel. Otherwise, removing it and filling it up entirely with the new medium will depend on your budget and how deep it really gets.