Always tempo map before fully charting or it'll all end in tears and frustration. Take it from a guy whose had to go back through a few of the beginning ones and redo the whole thing. Totally sucked.
Anyway, take a look at this current thread:
Although that's not my preferred method, it might resonate with you.
You absolutely do NOT need to put a marker at every measure unless it calls for it (I haven't come across any that have needed THAT much help). You should drop markers when needed, and that is usually when the beat doesn't align or it's slightly off (since, inevitably, it will start to spiral after that slightly off location). There are some songs where I've dropped a hundred and some songs I've dropped ten (usually heavily electronic-influenced music that programmed their drums). Really depends on how well the band plays to the beat.
Keep with it. That was the toughest thing for me to learn, but once you get it, it's not so daunting anymore.