Leveling in 5e when converting from Pathfinder is actually not that bad; you'll need to be careful (or use Milestones, like I do for my conversion) to keep the XPs up. Generally, I've found that you'll be falling behind just a bit in XP including just monsters, which leaves you a bit of wiggle room for xp rewards for quests.
For converting actual monsters, you need to do each encounter separately, and keep the encounter from being just a copy/paste, although you can grab a lot of tactics from the tactics section that Pathfinder usually includes in their adventures for each encounter. Converting monsters, though, doesn't really require that much of the DMG, because you have to basically make the monsters from scratch--I go the simple route and choose monsters that fit what the encounter is supposed to do, and there are a lot of monsters that are already in the MM for you to use instead. Special ones, like a Goblin Warchanter, is pretty easy to convert, just add the spellcasting ability from a Bard, and raise the CR by just a bit and bump the HP a bit. I've found that Surfarcher's Monster Analysis gives you a really good idea where everything should go--the DMG will probably replace that, but I'm halfway through converting Rise of the Runelords before I even get my DMG, using basically just the MM, since I don't have my DMG yet, and can't justify paying an extra 20 bucks (and I don't have a FLGS anywhere near me, anyway).
