Hey there! Sorry for the somewhat, kinda, sorta, definitely late reply! I'm no expert myself, and this is from experience during Season 1, but I can provide you a bit of insight at least.
1. I started out doing quests in the quest hubs described in the wiki. I heared that battlegrounds is a fast way of leveling? Does that mean questing there or PvP?
• Quests are tiered every five levels (1-4, 5-9, 10-14, etc) and are situated in the main town of a particular zone (or adjacent zone, such as Dartmoor's Quests being in Cornwall) or that particular BG.
• Most zones will have multiple tiers of quests, such as Camelot Hills having 5-9s, 10-14s, etc, so once you finish up one set, you can come back in the next bracket for more fun adventures.
• Battlegrounds have their own repeatable quests, and whompin' players is good XP. Capturing the centre keep is a whole level, but only once per BG (so you can get it once in Lion's Den, then Thidranki, etc.).
2. I heard that getting template items after 50 can get a bit grindy. I have a limited time span in which I can play (~21:00 - 0:00 EU time) and like to do things solo. I don't have anything against group play, but I like to play the gema at my pace and solo is usually more chill. Is it even possible to farm a full template solo? I don't mind joining a raid from time to time.
• Dragon raids tend to be done immediately after or very soon after the dragon spawns. I can't recall the respawn timer, because I've been away for a bit, but it was only a few hours, I believe, not 24. So you have a good chance of encountering a Dragon raid during your three hour window.
• Solo gearing would be a bit more difficult, but you can certainly do so, depending on your class and its efficiency. I've never done them myself (which I should), but I know there are solo quests in the RvR zones as well for rewards. It's much better to join raids, however, like the aforementioned Dragon Raid, Caer Sidi, etc. They provide different currencies in which you can select your gear to purchase, rather than relying on a drop and a good roll to win it. You may not win a piece of gear when raiding, but go enough times and you can just buy it outright from a vendor.
• Even solo, some classes are snatched up immediately when joining a raid battlegroup. Healers first and foremost, critical support classes next, and then the rest. You
can get groups as any class, though. Most BG Leaders will try and ensure that everyone has a group, in my experience. I've personally gotten reliable groups as a 'selfish' class that doesn't benefit the group at all beyond DPS, you just gotta be a bit charismatic and polite. Self-depreciating jokes help.
3. Where do I start once I'm level 50? What are general steps to get endgame loot? I guess farming some good ROGs is a good base? I would be open to creating a farming char like Necro (friar?) or BD if it means I can acquire items / currency quicker. What raids would I have to attend?
• Friars are absolutely amazing to farm up Stonehenge Barrows, and even whomp Reds/Purples in Dartmoor.
• Necromancers are good, but with support (Cleric/Friar) they really shine. You can certainly go it alone, however. Ditto with Bonedancers.
• Based on my wife's experience as a Friar, you get raid group invites pretty quick. With Dual Speccing being a thing with Season 2 as well, you could even have a healie raid spec instead of having to sheepishly go 'I'm 50 Staff for Excommunicate...'.
• Excommunicate is pretty awesome, though. Can't blame you there.
• Dragon Raids will likely be your first jumping off point to raiding. Then Caer Sidi/Galladoria/Tuscaren Glacier. Other SI raid dungeons can be done, but they're less frequently done. Could even get into a Sobekite Eternal group as well, if you're what they're looking for.
• If nothing else, get your salvaging up, farm, break items, get money, buy loot you need.
4. Any guilds around that are active in my playing time?
Maybe even some old Stonehenge people?
• Good luck finding folks from your home server. ♥
• Eden players are a friendly bunch (for the most part), so finding a guild that suits your playstyle/time isn't difficult. Unless it's a roleplaying guild. I'm still looking for one of those.
I am not sure if some of this information is out of date and wrong, but overall, playing here solo is very viable, even if you're only on for a few hours a day. Definitely would recommend a Necromancer/Friar/Bonedancer for solo play, though you can have a go at it with other classes as well, such as Paladin, Warden, and Valkyrie. They just won't be as efficient and/or awesome, but can find groups with ease when needed.
Either way, welcome to Eden!
