As someone who acquired 400M souls on his Silver Knight cosplay character through nothing but invasions, I'm going to try and be unbiased here.
It mostly scales with DEX and not only that, it stays at a C scaling for it and only E for STR. Nearly everyone likes to pass it over. It uses Twinkling Titanite as well, making it more difficult to upgrade. Would you spend your creamy twinkles on a weapon you're unsure about? I wouldn't.
Now for some positives. First of all, its base damage at +5 is fucking 262. Even the longsword at +15 has only 200, but that makes up for it with a C/C scaling. As others have said, it's a rather long straight sword, making it easier to catch players and enemies. I like it for PVE, but in PVP it can be a monster. Its strong attack can stunlock for two hits. 262 + your DEX (52% scaling) + 1.5x damage boost from two-handing, then add on top of that the massive bonus damage from your weapon buff, in this case Darkmoon Blade. I used to kill players in two to four hits with that thing and that was without a buff. Many people like to look at scaling, but that isn't everything. The moveset can really set the pace of a battle, especially if the other player is unfamiliar with it. What matters is not being predictable with your attacks.
No, I suggested heavier armor. Making a theme for your character is fun, trust me I know, but you're also bringing PVE into it. Those robes aren't going to protect you. You need a set of armor that provides more defense and poise, but still allows a fast roll though medium rolls can also be fine if you know what you're doing A common medium armor set is the Elite Knight set. It can give you some poise you need, meaning you can either unequip the Wolf Ring for maybe Havel's if you don't have the fast roll with it, or for another ring you'd like. Alternatively, you can keep the ring for the extra 40 poise. You already have the Ring of Favor so a fast roll shouldn't be difficult.
First of all like you said, increase your VIT. With the data others and myself have stated to you concerning weapon damage, you should know by now that you will either be one or two-shot as you are now. You also definitely won't survive a normal riposte from many weapons. You need health for PVP so you can be allowed to make mistakes and/or trades. Your poise won't mean jack shit if you die in one hit.
You seem pretty hellbent on the whole 120 thing, but understand that's just the community PVP level. When you feel your character is complete, it's better to stop than invest in stats you don't really need. My own Forest Ninja character stopped at lvl 108. My FTH/STR build stopped at 128. As long as you're around that level, it won't make much difference. Honestly, you're invading the forest anyway, which means you're invading 10% below your level and infinitely higher. You can still meet Big Bubba, there's just less of a chance of doing so. Be wary of Killing-You-Guy, the lvl 710 destroyer of worlds
As I said, it might be best for your first character to be the experiment. I still have my first level 288. I never PVP with him, but I can experiment with any weapon/armor/spell combination I want when making another PVP build. If those are the two options you want for your stats, then the 30 VIT 30 FTH is preferable. 30 is the soft cap for VIT and you should have about 1100 HP for it, but 1000 at 27 is enough in my opinion.
Dragons are simple, get the stones and have a dragon weapon. The End but Kalameet's is my favorite. For your Ninja, I'm guessing you'll use the Shadow set? Know that you'll have no poise at all, which is fine. You can either play carefully, or if you're not doing the Forest Ninja cosplay, use the Wolf Ring. Washing Pole is fun, but it has the worst scaling of the katanas and breaks the easiest. Just be prepared. I think that's all, rate my wall o' text.
I really like how he looks but can he actually breathe in that?