if you're reading something as big as capital you can also read someone like Cleaver or Harvey, etc, at the same time. They don't always go in the same chunks or pages as you want to but there are a few guidebooks that match the main chapters and sections
main thing to watch out for is the anti-marxist intros like Singer. they can be useful but you can't let their criticisms put you off because the criticisms are weak
later on it could be a good idea to quickly look through For Marx by Althusser. this will give a good idea about how much someone can get out of Theses on Feuerbach if they study it carefully and research around the topics.