For mission 44 I grinded up to 2.6 million gold and maxed out my banner that way from level 24. Mission 78 I grinded I think 2.4 million gold and got my castle from 37 to 78 as you see in the screenshot. For my items, I had 11 maxed out (999) items from grinding that much. Got about 110 cakes (mainly thanks to the roulette) and had no problem upgrading stuff towards the end leveling process.