Struggling a little with how to balance this idea.

Relative comparison points might be Monastery Swiftspear, particularly with (((Doomguard Champion))), Rustwing Falcon for precedent for 1/2 with an ability for 1 mana at common, and Gearsmith Prodigy for a newer common that's a 1 mana 1/2 that gets +1/+0 as long as you control a (Cardtype).

Another factor that plays into the power level a little is that gates, as lands, don't cost mana while things like artifacts or other permanents do. On the other hand, Gates are a specific and somewhat parasitic category. The classic comparison here really is Kird Ape, which is based on an off-color basic land type and gets +1/+2 as a 1/1, which is less parasitic and has a slight edge in the toughness department. These are sort of better but not better Kird Apes, in that they get an ability but are a little more specialized and function as 2/2's.

I've decided to make these 1/1 commons. If it feels pushed I'd consider rolling the creature ability into the "as long as you control a Gate" section.

I think the largest problem of this cycle right now is that a 1/1 for 1 is just not what this would want to be in every color. Surely in white this can be a key card to enable an aggressive white weenie strategy, but other colors have different needs.

Yes some of the other colors like Blue are more defensive or otherwise less interested in weenies. The relative balance feels off most for the Blue and Green ones to me, especially with Trample feeling off for a weenie creature and Hexproof clashing with the offensive feel of what the cycle does. Black and Red feel decent enough to me.

So what I did is I got rid of the other designs except for the red one, renamed it to be relevant to the Harmonium - Harmonium Zealot - and now this a pair rather than a cycle. and the Harmonium get a weenie archetype, so it's fitting.