Before you build bike, you may want to consider rust prevention measures for the steel, which is uncoated on the inside of the tubes. Some use an aerosol rust preventer such as Weigle Framesaver. I've built several bikes and always rustproof steel framesets with boiled linseed oil (sold in the house paint section of the hardware store), because it's cheaper and more thorough than spraying into a couple frame holes. It requires patience, an outside work area (for spills and curing) and about 3-7 days for the coating to dry. I've used paper formed into little funnels to direct linseed oil into small bottom bracket holes, but a pistol oiler and appropriately sized tubing is neater with less waste. Here are some old comments on this topic.

You may want to consider a Salsa Alternator rack for the Marrakesh, whose high rack mount points force a conventionally sized rear rack to sit ~8cm higher than normal.

Someday you'll have to put a Rohloff Speedhub on that frameset to justify those sliding dropouts. Please share an image of completed bicycle.