I started tracking my BO1 Arena games today. Out of 35 matches, I faced 8 RDW, won 50% (4 matches). I think the matchup overall is about 50-50, maybe 55-45 in Golgari's favor, and your win rate goes up if you get at least one life gain off Wildgrowth Walker. The 3 out of the 4 games I lost I either didn't have access to one color, or never got off 2 lands. (I might need to mulligan better or add more duals - I've been saving my rare WCs so I only have 3 shock 2 check)
I've played both decks on Arena; red has some explosive hands, but has a tendency to run out of steam. If they get the nut draw, there's not much you can do, and you'll be down to 6-8 before turn 4.
Having wildgrowth isn't necessary to win - 2 out of my 4 wins I didn't draw one.
The ideal opening hand has 2-3 explore creatures (ideally two 2-drops, squire is preferred over branchwalker and a jadelight) to ensure a steady flow of lands. On turn one you play an elf if you have it, even if you have to use a shock, because they'll bolt it everytime, and 2 <= 2-3. I kind of wish I had been tracking who was going first - I suspect it matters a lot, I'll do that tomorrow.
You want to play creatures on turns 2-3 and just assume they're going to die. You want them to waste their burn spells on your creatures. Play wildgrowth last, but if he's your only guy, it's okay to run him on 2 (especially if you have Find to get him back later).
When exploring during the early turns, send to the graveyard Tyrant, Karn, big Vraska, or Vivienne, those won't be much help. Getting more creatures is better, just make sure you can play them.
You're going to stabilize at around turns 4-6, with around 6-10 life, and hopefully the red deck's hand is spent. 6 life is scary - you're basically hoping he doesn't have two bolts, but it happens. Stay scared, never attack without leaving a blocker for a hasted 2/2 mage. You're hoping he doesn't draw LUtS, Risk Factor or Frenzy (frenzy is the worst for him, light up is the best)