1st: Grind dont get bad til you are around lvl 71 or so
2nd: You dont have to do raids, most of the time raiding, cost outweighs benifit.
3rd: Neutral zone is a territory on the map located between Dark elf Village and Elven Village. The keeps you are reffering to might be fortresses? Like siegable clan halls (offers buffs, %-rez etc).
4th: Nothing like battle ground, but there is a small arena located at the monster race track (accessible from any non-starter town gatekeeper for free).
The grind on this game is alot more severe than WoW. Takes a week or so to get to lvl 70 on WoW. Here it takes years to achieve top level. I dont think anyone has reached level 85 yet..
First, I hope you're not already 'grinding' at your level. There are quests that you can easily follow and complete that will boost you right on up through the levels till 20. If you do it right, you'll skip several levels every time you complete one of those quests. Just do what the newbie guide tells you. You really shouldn't even be killing mobs yet unless you're completing one of the quests.
Raids actually will shoot you up through the levels quickly, but will leave a new player lacking in adena, which is just as important (if not more) than levels. Plus, finding a decent group of people your level who actually know what they're doing and are on at the same time as you can be difficult. So basically, don't worry about raiding.
Neutral Zones... well, if you're talking about THE neutral zone, which is in between DE and LE villages, it's just an area of the game, nothing special about it. Peace zones, such as towns and a few other spots in the game, are areas where no one can attack another player. Outside of those areas (basically, 90% of the world) anyone can attack anybody at any time for any reason. Keeps? We don't have anything called keeps in L2... we have Castles and Fortresses, which can be sieged and taken by clans.
You started at a good time, use the common items that seem to drop alot. No one has ever had the ability to use common items until this recent update. It used to be that everyone used piece of crap weapons that were always in need of being upgraded. Atleast now you have the ability to get the upgrades at a reasonable cost and time frame. Up until S Grade that is. S grade should be difficult to get imo.