Story mode dungeon and World Chat
I’m afraid you should plan on bringing a full party to story mode dungeons. Story Mode dungeons are a lower level than Exploration Mode, but they’re still designed for five people.
Just a tip, you might have an easier time finding a good group on the LFG tool if you write something like “Casual, watching cutscenes, having fun!” or something like that. Dungeon players range from hardcore speedrunners to new players who are afraid to do dungeons, so you’ll have a better time if you advertise for players who want to go at the same pace as you do.
Map chat is only for the current zone. There is no world chat channel.
Story Mode: This is designed for a party of five.
You do Story so that you can thereafter open it in Explorable with that alt. Also if you do them in order, you get the story of Destiny’s Edge reforming. You get XP but no dungeon tokens. Story is generally easier than Explorable and is tuned to 5 levels lower. So each 5 levels starting when you get Ascalon Catacombs story you get access to Story, then Explore, then Story of the next tier up, etc etc.
You can do Explore without ever touching Story, you just need someone who has done Story to open the Explorable version. The events in the Explorable one are a narrative continuation from what happened in Story. Eg in Caudecus Manor Story, you attend a party with Logan in which things go awry and the Queen is kidnapped. In explorable, you’re there for subsequent mop up and further storyline that doesn’t involve Destiny’s Edge. You also get tokens as part of the reward, which you can trade in for exotic weapons and armor of various stats with skins unique to that dungeon.
World chat: No, there is no global broadcast. Map is just your current map and only the version of it you’re in. If you join a friend in another version of Diessa Plateau, you will switch to new Map chat. You can see your guild chat anywhere you are, but that won’t give you thousands of people talking (yay! chat spam can suck!).
I’d be glad to help you in any dungeon you like, if you are on NA and if I can be in game when you need me. I’m pretty sure I can scare up others who want help; if we PuG, we just need to say “teaching run, watching cinematics” to help make sure we don’t get impatient speed runners and you can watch the story parts.
Most dungeons can be technically completed solo, but they will always be (regardless of how many party members you have) scaled to 5 people. If you are a really good player (it might also help to learn some tricks from videos of other people soloing), you might actually finish some paths solo, but for a new guy I would definitely recommend to find a party. I also highly suggest to let other people know if you’re doing a particular dungeon for your first time, sometimes people expect to go through smoothly without much or any explanation. Look for “everyone welcome” parties or make one yourslef and you should be good to go.
Also as stated above, map chat is specific to the exact map copy you’re located in. Don’t worry though, most maps are usually quite populated and you will get an answer shortly after posting any reasonable question in map chat. If you’re looking for a more “lively” chat, it’s usually the cities (Lion’s Arch,…) because people there generally have nothing else to do but chat.