I have an i3 MK3 as well, and I don’t use rafts, at all.
for just floors: no brim, no raft. there’s enough surface material anyway, and it doesn’t get top-heavy.
for walls: I turn the brim on, the default brim that can be selected with the layer heigth setting. the walls sometimes get top-heavy, so a bit more surface area helps in that regard.
while floors can be set to quite a low infill percentage, I also found that 15 to 20% infill (depending on the temp in the room. if its low, I can go to 15..) works best for walls, no lower, because otherwise some of the layers near where ‘bricks’ in the wall meet curl upwards due to not cooling enough, causing the printer to hit them, and toss the wall over.
with that in mind, I’ve printed several-day long prints of castle walls, with the entire plate filled up. I’m expecting the walls from the clorehaven kickstarter to go significantly easier and faster, especially the tudor walls, because there’s far less layers of bricks that need to be prepared for. if you want, I can give an update on that once I try them. 🙂