I'm not there yet, but with the completion of Adventure Mode I'm quite close to the current 100% of Hyrule Warriors Legends. Of course with future DLC there will be more stuff and the rule of thumb with Hyrule Warriors is that you never will be really done with the game, unless you are crazy determined with lots of free time at your hand.
Anyway, this is what I've achieved so far:
- Beaten Legends Mode on Easy, Normal and Hard.
- Unlocked all characters, weapons and costumes.
- Collected all Heart Containers and Pieces.
- Found all Gold Skulltulas.
- Unlocked all fairy clothings and food.
- Got all available fairy slots.
- A-ranked every mission in Adventure Mode.
- Unsealed both Master Sword weapon skills.
You may as well call this the "fun part", because what's left for me to do would be the following:
- Beat Legends Mode on Hero difficulty.
- Get every character to the Lvl MAX.
- Craft all badges for every character.
- Get all the medals.
You may as well call this the "grinding part". At least I'm quite close to having all the badges. There is a shortcoming of materials from the new Wind Waker contents, because the four Adventure Maps from the Wii U don't use the new enemies. Luckily the Koholint Map helps out with this situation thanks to the possible double drops and some good missions featuring Big Blins, Stone Blins, Helmaroc Kings, Phantom Ganons and the new characters.
I also have the majority of medals, only very few are left. One requires you to create and use every mixture at least once, but I won't go through with this until after all characters are available and I have an overabundance of materials in all colors. There is also one medal that I will probably never get, because it wants you to rent 50 Rental Skills via a local connection, but I don't know anyone with this game in my proximity. That might change, however...
Leveling everyone to Level 150 now and later to 200 and 255 will probably take the most time, because leveling is significantly slower on the 3DS. On the Wii U you can abuse the Rupee Glitch, but there are also very fast leveling missions like "Rack up your KO count 12" on the Master Quest Map's low left corner. That one has been nerfed in Legends, however, above Level 70 the gained experience gets a lot lower. But maybe future DLC Maps will offer some good experience pots. And I have played these missions so many times with everyone on the Wii U, it's sickening. I'll just prefer playing my favorite characters everywhere and then buy levels for other characters from selling weapons, which is your best income.
And I will play Legend Mode on Hero difficulty with my favorite character(s), as soon as they reached Level 255 and have their best possible weapons. I will do this in Free Mode and there's no reason to attempt this earlier. It will just be tedious otherwise.
Weapon and fairy building is also something that you might want to do, but I view this as optional, because both weapons and fairies are in a state of flux. You can always sell or release them, so nothing is really permanent here. Ask the guys, who build themselves super awesome Level 4 weapons, only to learn that we'll get Level 4+ variants with the DLC.
The only things that I view as necessary for a 100% completion are unlocking all the weapon tiers, unsealing the Master Sword (you can't get rid of that and it unlocks the Legendary seals), having all fairy slots, getting all the fairy clothing and getting every fairy food at least once, so it starts dropping randomly (like weapons). But what you do with the weapons and fairies is really up to you...
On the Wii U I was quite invested in creating "perfect" weapons (see here), but in the end it never really was worth all the trouble, because I'm not using them. My plan was to A-rank Challenge Mode with every character, where best possible weapons certainly would be useful, but that mode is just way too tedious and only fun with characters that are good at taking down giant bosses. So, in the end I never really bothered and I probably won't invest in the Wii U version any further, save for checking out the new characters in better graphics.
On Legends I still try to unseal good skills for everyone. Hasty Attacks is usually nice to have and I might be willing to unseal a Legendary skill with everyone by just plowing through everything again. It's fun to go through the Adventure Maps again and just farm Item Cards, if you don't have anything to lose and don't have to worry about A-ranks. On the Wii U I actually cleared all Adventure Maps of all Item Cards (they stop appearing after you got 5 of each), and I might do the same over the course of the next months, while I unseal weapon skills.
At the same time I will probably grind lots of fairy food and try to get at least one fairy that has all Rental Skill available. I don't view this as a must, however, since I usually just use Water Wall and rarely Repair Technician, which are easy to get. The golden Rental Skills, which probably take multiple refreshes, don't seem to be worth the trouble. Only Magic Fountain sounds nice to have, where I want to get it and try it out for myself in the future.
Anyway, now that I have all the costumes available and can freely reign over all the Adventure Maps, the grinding part won't be too bad. Grinding is more annoying if you have to do it in order to proceed, but luckily this never really has been the case in Legends. From now on I'll just play casually every now and then and maybe focus on one character per play session. There's no rush, the next DLC is still two months away.