I have just started training for my first Ironman. I have done 3 half Ironmans and many shorter distances. I purchased a 20 week Training Peaks plan that is structured for beginners. Depending on the week, the time required to train, per the plan, is between 8 hours and 18 hours.

Regarding swim, some races are easier to swim than others. There are at least a couple that the swim is with the current (point to point) and results in fast swim times. Some swims are wetsuit eligible which increases buoyancy, also resulting in a faster swim than without a wetsuit.

My suggestion is to look at the available races and pick the course that is optimal for you. You can search for training plans on Training Peaks. I have done a few race-cations and they have been a lot of fun.