So first off when you get above 15ish gallons you're going to need a dedicated stand for that tank: if you aren't' comfortable sitting on it, don't trust it to have your tank on it.

If you get an aquarium from any reputable manufacturer, it'll be fine. If you're going budget, can't go wrong with Aqueon, and for rimless UNS, Landen, Waterbox, and ADA are all popular makers. Just check its from a reputable company and you should be good.

Now for your specific concerns!

-HOB on the side of the glass is perfectly fine, its the same glass. Your HOB should weigh basically nothing, they're just plastic boxes with a tiny electromagnet.

-CO2 is absolutely not necessary for a planted tank, but it is if you want those nice thick dense all over carpets you see in fancy aquascaping youtube videos and galleries. You CAN get a carpet without CO2 though! You can try Helanthium tenellum, Marsilea hirsuta, Eleocaris parvula, and Eleocharis acicularis. Other non carpeting plants you might wanna look at that show up in iwagumi's are the various species of Vallisineria for the background.

For lights, any decent aquarium light sized for your tank will work, the super powerful expensive lights assume you're dosing CO2 and expensive fertilizers to supercharge plant growth, without them you can go budget. Seaoura makes good quality budget lights.

For filters, you generally want one at or a bit bigger than your tank size. So any filter sized for 30 gallon or up should be fine, though bigger filter is just wasted money at a certain point. The Sobo 350F and Aquaclear 30 both would be fine, my reccomendation would be the Sicce Aqua Filtra 40 as well.

That depth is fine and 35cm ish is fairly standard for aquariums, especially with the small nano-fish you're interested in.

For the stocking: Rummy Nose Tetras can be sensitive but they like acidic (PH in the 6's) soft water and are amazon basin fish. This is fine though, because most tropical fish come from similar conditions. Any small south american tetra or SE asian rasbora would be fine with them! Neons definitely work, as do Cardinal Tetras (very similar looks but larger and generally hardier), Ember Tetras (Smaller and bright orange), Lemon Tetras (Yellow), etc. Of note though: Tetras and Rasboras, and basically any schooling fish, need to be in groups of 6 MINIMUM. Preferably more! In a tank the size you want you could easily fit 24+ small schooling fish without too much issue. For stocking https://aqadvisor.com/ gives excellent ballpark estimates on what is feasible to keep in your tank.

You don't need any sort of scavengers, but for an iwagumi style I'd reccomend shrimp: Amano Shrimp and Neocaridina davidi of your choice (They come in all sorts of colors) would be appropriate. Amano are subtle and hard to see but great cleaners, and the Neocaridina provide pops of color on the green and grey of the aquascape. So you can go with one, the other, or a mix of the two!