Welcome to NS Iris!!!
First of all, joining NS as a complete newbie is gonna be a bit difficult in some way. You're going to be pressured to level to 84 or 85 quickly, since most end game material is more enjoyable at that level (84 ish cause of Battlefield - harmless PvP). You would be grinding a bit; meaning doing lots of quests/wanted papers. Crafting to up your assistant skills and farming certain items to sell to earn some money. XD Fun life! And ofcourse getting used to your game skills~ XD
Population wise: Theres loads of higher levels rather than low levels. Basically its easy to level in the game so far. You'd have no difficulty. Also theres a few people who love helping around taking newbies to dungeons and showing them the ropes -- *cough* Im one of them~ --
Generally to gear up, you would start at around lvl 60. 1-50ish is still pretty easy with whatever you pick up + mailed items (you get free stuff in mailbox when you level up enough). At lvl 60-65, its better to have epic gears since you would be entering pvp zones more to do your quests. You'd need extra attack and protection to be fast and undetectable. (Dont worry not all of us harm ya'll LOL!)
Generally all classes (cept Priests/Sages) are okay with solo-ing. People lean towards ranged classes, gunners or magic users for levelling sicne it doesnt require you to move often when killing. Healers are okay for the first few low levels, unfortunately you might need help to continue 65-85 levelling. This is pretty gruelling, even for high damagers. XD Go make some friends!
Some of the moolah gears are also attainable without spending moolah. Stat V cards for example drop from dungeons like Lisk Hard/Insane and Golden Temples. Wings are generally perceived to be necessary in higher dungeons and pvp since most people have it already; but you can play the game well even without it ^^ I know a few priests who enjoys playing even when she doesn't have wings (Titles that give 25% Stat, 25%Attack/Hp, Speed etc.)
Dungeons are soloable when you get decently geared or higher in level for it. And example is CN. CN is a lvl 15 dungeon. If you're anywhere in lvl 15 - 20 you cannot solo it without dying a few times XD!!!. But if you're already 21+ then its much much easier to solo. ANother thing is if you're properly geared (dont do this for lower levels its a waste of time unless youre super lucky~). But in higher levels; lvl 75 can solo lvl 70-75 dungeons easily. But it depends.
Some dungeons are built to be able to be solo-able. While others are built to need at least a few people or more. =3 Dayum I typed a lot, you just had so many awesome questions XD!
Hope to see you ingame~ If you need anything pm me on it >D
IGN: RayDarkwolf