Just finally got around to setting up Pi-Hole on a Pi 3 and routing my DNS to the Pi. Curious about a couple things.

1. I don't expect it to take the whole 8 GB of memory from the Pi, but how big do the logs get for Pi-Hole? Is there a way for them to trash (say, after 30 days) if it gets too big?
2. The Pi is already on 24/7 running a couple other scripts, including two Twitter bots. Not sure how memory intensive they can be. Seems like right off the bat, the Pi is at 60% CPU load according to Pi-Hole's dashboard. Is that going to be a problem?
3. How will it affect internet speed? The Pi is hard-wired, but I've got a lot of network activity, including a home server/seedbox, and in combination with the CPU load mentioned earlier, will my internet take any notable hit?
4. Just in case, is there a way to have a fallback for my router in case the Pi should fail or go offline? Using DD-WRT and I've got DNS 1 and DNS 2 set to the Pi's IP (non-static, but I'll deal with that on my own if my router ever goes down). DNS 3 is currently 0.0.0.0. Could I set up a fallback on DNS 3?

Thanks for all your help! Looking forward to the ad freedom!