I've never used editing software so can't help you on that front. But I'd question whether it is worth it for a rough draft of a first novel. You've got plenty of drafts ahead before sending it out to agents/publishers if that's what you're planning to do, so if you're going to pay for any line editing, you might as well wait until you've got to the final draft and everything is as good as you can make it.
If you are planning to submit to agents or publishers, then actually things like comma splices aren't going to be deal breakers unless they're occurring in every line! What agents etc are looking for is a good voice, interesting characters and a gripping opening and plot. If they get hung up over a few misplaced commas in the first pages, then that's because they've not been caught up enough in the story to overlook the errors, which means you've got a far bigger problem than punctuation.
One reason you might be missing the splices and passive voice in editing, though, is because you are reading too quickly and jumping the words and punctuation in your rush. One way to overcome that is to read aloud which forces you to go more slowly and look at things carefully. Another way is to read backwards -- literally start with the last sentence and read that. Then the penultimate sentence, then the one before it etc. Your eyes can't jump ahead to the next line, because the next line you need is higher up the page, so your brain stutters and has to concentrate more on the line you're on, which is what you need. Another way is to look at each paragraph as a discrete entity by physically cutting and pasting it to a new document. That will then allow you to concentrate on that paragraph on that otherwise blank page, instead of rushing through it to the next para -- and changing font and font size also helps trick the brain into thinking it's something new, not the same-old, same-old and therefore to be ignored. Once you've edited it there, you take it back to the master file, then cut the next para and take it across and so on. It will be a slow process, but that's the point -- you need to slow down to do the job thoroughly.
