So aside from all of that business about the bacteria (who will find their way to an ammonia source but who do not live in the ammonia bottle), redundancy isn't a bad idea but Eheims enjoy a reputation for rock solid dependability and an HOB will drive off a certain amount of CO2. If you want a planted tank (as opposed to a tank with a few plants) CO2 and lighting will be issues -- lots of friendly help in the plant forum.
What's the difference? Just a matter of degree and of focus… You sound like someone willing to do the research and the work. I personally think fully planted is so
incredible that its worth the extra effort and expense, but be prepared for both.
As far as stocking goes, here are two ideas you may find interesting…
You'll want fish that are compatible but you'll also want a fully involved tank -- think about where the fish will spend time and how they'll vie for your attention. I tried to get a few bottom dwellers, a few schools of small schoolers for activity and one pair of centerpiece fish. There's harmony as far as behavior but also in terms of appearance and general mix. A lot of beautiful fish may wind up looking like a jumbled up mess or like a natural community living in this particular slice of water that somehow wound up in your living room.
You might want to look into running a regional tank or even a
biotope. Not for everyone, but fun for the research obsessed. I went regional -- I liked a lot of SE Asian fish and the water was similar to my tap so I went with that. You may find it interesting and it may help give you a better focus.
Either way or a different way you'll want to be careful with the wish list books. I did the same thing and got my heart set on some mighty obscure little fish. So sad
. Availability and how far you'll drive for a couple of little fish are limiting factors. This
directory may help narrow the search. It got me to all of my favorite fishstores here in NY.
You sound like you're off to a great start, good luck and enjoy, and welcome to AqC