I can't give any good answers, you'll need to wait for others for those, but I can give you half answers for starters.
- If you don't find a word or any close substitute, you're probably out of luck. The word probably just isn't known yet. Our Valyrian scholars are pretty good at coming up with speculative derivations, but for anything reasonably solid you'll need to a) wait for the word to possibly come up (we're getting words pretty fast now that the season is rolling on and has a fair amount of Valyrian in it, but ascertaining what that all really says will take some time) or b) try asking David (he's really good at keeping himself busy, so don't get your hopes up on that, but he does sometimes answer stuff on both tumblr and twitter).
- I'm not sure how far you think you are on your translation, but it looks you have a long way to go, even ignoring the missing two words. Valyrian has a very different word order and deals with a lot of things with suffixes when English uses words. Just throwing away the words you probably shouldn't translate separately and rearranging the remaining in more Valyrian order gives something roughly like "ours is what that fire blood back take and our enemies screaming die". It's also good to keep a close eye on the sense in which each word is translated in the vocab page. Inkon is a noun, so you should expect it to denote to the posteriori side of a person, so that is unlikely to work for you; arlī is much more promising, as it's marked an adverb and that's the kind of sense you need. Skoros is a question word, so it might be off too. And mixing High Valyrian with Astapori Valyrian with no adjustment is also rather iffy. Though as dos should not be needed, maybe that mismatch disappears naturally.
Welcome and good luck going forward. Learn to love the challenge, because we have that in spades.
