New to fish and weighing my options..

[Norm66]

I'm assuming you're going with cichlids (yellow labs) here. If not the rock information that follows isn't necessarily the case.

I recommend the middle sized Emperor (not Penguin) power filter (or HOB for hang-on-back) but the middle one, not the smaller one even though the box will tell you it's for a tank bigger than your 30 gallon. More filtration is better, especially for cichlids.

Substrate. I prefer sand. You can buy a 50 pound bag of pool filter sand at a pool supply store for less than $10 versus what you'll pay for gravel at the pet store. Plus it looks a lot more natural. Additionally waste sits on top of the sand so you can sweep it up whereas with gravel it goes down into the gravel making it harder to clean up.

Rocks. Cichlids live in a heavily rocked shoreline therefore they like/need quite a bit of rocks to be happy. Whatever you do, when you set your tank up put the rocks in first, get them arranged how you like them and how they are stable and then add your sand. This is because cichlids dig and obviously if the rocks are on the sand and the fish dig the sane up....well the rocks will fall over. Despite what you may read there is no need to put anything down on the glass before your rocks. The glass is more than strong enough to hold whatever amount of rocks you can fit in there. Plus like I said the fish dig and if there's something down there you'll see it and it'll be ugly.

Heaters. They're all terrible IMO. I use Ebo/Jager heaters and (knock wood) haven't had a failure yet. It's important to get an underpowered heater because when heaters fail, they inevitably fail and stick on. If the heater is over-powered and sticks on it'll kill your fish. I had a two month old heater try to boil one of my tanks. I got saved by a fluke of touching the glass and noticing it was hot. Thermometers are a cheap and very worthwhile investment. The stick-on kind aren't that accurate but they're close enough to tell you if there's trouble.

Tops. Buy glass tops, not the plastic ones. It'll cut way down on evaporation and they just look better.

Lights. Fluorescent or LED. I use both and like them. LEDs are still expensive but nice.

That's all I can think of. Feel free to PM me if you have any questions. I'm happy to help.