For a deck that uses more than one color, lands that can produce more than one of those colors are great. It's very frustrating to have good cards in hand but being unable to play them because you don't have the colors available. The more colors you run, the more likely that issue is to occur. So you should aim to play only as few colors as are nessessary. As a beginner deckbuilder, you should stick to two colors at most, until you have more experience.
From what you wrote, I don't think that branching out into green just for big creatures is a good idea (you're already considering some big red creatures anyway). Some compelling reasons to do so nonetheless would be access to enchantment removal and mana ramp. Which
Evolving Wilds 
is not. I think you are misunderstanding something about that card. It's mainly color fixing at the cost of tempo, which is still great.
Going green can still be very viable, it all depends on your intended strategy. If you want to win with some big but costly creatures, cards like
Cultivate 
,
Rampant Growth 
,
Dawntreader Elk 
, etc. will get them out faster. Especially the elk and cards like it are great here, because they provide early defense as well.
What are the black cards you're considering? There are a lot of great removal spells in red already, so it should be unnessessary to go black just for
Go for the Throat 
for example.
