Welp, was asleep.
To answer some questions
Party size is based on individual preference. If you are strong enough to still kill easily when you are in a party, then go ahead and play in a party. There's no reason to solo, unless you can't handle the higher hp/more spawns from party.
By can't handle, I mean it becomes less efficient. Since I'm unsure as to how strong you are at any point in time, I cannot comment on specifics.
You can solo even if you are not a spear. The thing that you have to ensure you do is find the right skills and play carefully/correctly.
Sometimes, you may need to switch weapons for this tactic. For example, if you don't have Oni Spirit Blast extracted on sword, or have found another really good AOE spell, you may want to switch to Odachi, or spec for an ougi so that you have more mob potential.
@ Zetsumei
Keep in mind that my gear is far past the min limit required to do this map effectively.
To do it effectively, you need ~ Lv. 50 weapon + 50 or higher and as much possible skill force magatama. Accessories are not really needed.
Too lazy to screenshot all maga, but at the time, I had
Gemini x 2
Cancer
Peerless
Please keep in mind that you should choose magatama based on your weapon skills.