Finding what condoms work best for you can take a little experimentation, and you may want to get a few different brands and test them out to see if they're comfortable (plenty of people have curved penises, and condoms are flexible enough that they can account for that without issue). As far as size goes, width is often more relevant than length; a penis on the thinner side may need a snugger fit, while a thicker one may a need a wider fit.
Not really, no. After all, a perfectly rod-straight erection is actually less common than one with some natural, small degree of curve. Latex, which is what the majority of condoms are made of, is very thin and flexible, so any kind of condom will work just as well for a penis with a curve as it will for a penis without one.
You may not be able to get an exact measurement, though with a soft tape measure you could measure both width and length pretty accurately. But while condom size can matter in some instances, like someone on the thicker end finding a snugger fit is uncomfortable, most condoms can accommodate a range of penis sizes, so you can find ones that fit without knowing your exact length.