Any aquarium question works for me :p
1. I feel IAL is beneficial to lower the Betta's stress and encourage scale and fin regrowth. It also fights off bacteria. It is also beneficial for spawning and to Betta fry, encouraging microorganisms to cultivate for the fry to feed on.
2. I prefer my leaves whole or halved. I have not tried crushed bt probably because I feel it may be a heck of a lot messier. I have seen the bagged versions and may try it sometimes. But I like the whole because as it breaks down it introduces a lot of beneficial critter (such as infusoria). I have never heard of the seeds!
3. My favourite breed... Halfmoon plakat. No wait! Doubletail.

4. Because of the unique look they have. As long as the fella can swim, we are good to go. (Hence why I didn't choose HM)
5 I do not have any wilds though they do sound interesting. Perhaps one day I'll look into getting some.
6 I own: 1 EE, 1 DTgeno, 4 CT, 3 PK, 3 giants (or half?), 2 HM, 2 DeT, and no wilds. Not including the two Cambodians from one spawn I'll keep to continue to breed. And two DT from the other spawn. If you mean how many are mine personally and that I'll keep after they retire, I won't be keeping them all

i probably keep about 3-5 and a sorority.
7 I'd say... A tie between Anubias and Java Fern. Those suckers are hardy! They don't need a ton of light (great for spawn tanks that do not have heavy lighting), and repopulate themselves. :p
8 I have done DIY sponge filters before. If I had the space to work with I'd do some strip lighting over a series of tanks, reducing the amount of words that flow around here lol. Currently just use the lovely light that comes in to reduce expenses.