Newish player looking for help

Hey ya'll. I say newish because I have played GW2 before. Granted it was ton of time ago. I bought the game when it first came out, played for 6 months then didn't play again until recently when I came back. When I played before, I never got higher than level 65. I did delete him when I came back and recreated and leveled him to 80. It was a ranger. So here goes questions:

1. If I don't have one of the two specializations in my build at 80, am I setting myself up for failure? I honestly don't like either of the specs available for rangers.
2. I purchased the HoT/PoF double pack and got the 2 insta-80s. I did wait until I finished leveling my ranger to 80 just to get a feel for the game. After a little bit of research, I went with a thief with the sole purpose of Deadeye. At first, I used the rifle but after feeling that the unit was lackluster, and reading a rather large thread of the Thief forum, I switched to Double Pistol. Sorry. I rambled. Question is, should I give up doing all the different zones and go to HoT/PoF to level masteries etc?
3. Speaking of Masteries, is there enough points to master everything or should I be planning the points I spend?
4. Also on Masteries, the ones I've seen seem to be fluff or for crafters, are there any that are actual useful?
5. Now that I'm 80, besides doing all the zones that I didn't do, what else is there to do? What's the endgame in GW2?
6. Guilds, someone out there have a guild for a gamer that doesn't want to Discord, just have a guild chat to occasionally chat in?

Game is pretty fun. I still have 1 more insta-80, just not sure what to use it on as I'm enjoying the Deadeye.

Thanks for any help ya'll give.

1 - I don't know ranger well, but prior to PoF since druid was primarily a healing spec, the better damage builds were core builds. However, Soulbeast is also a damage spec and, as tends to be the case, the elite is stronger than the core spec that serves a similar function. If you're planning to participate in high end content (raids, T4 fractals) this may become an issue for you. However, for anything else (PvE-wise) I imagine core ranger is perfectly adaptable. Ranger tends to be a fairly forgiving class, and is often recommended for new players.

2 - Each area (Core, HoT, PoF) has its own set of mastery skills which may only be unlocked by playing the associated content. In order to train a mastery, you will need to earn mastery points as well as experience in the associated area. Core and PoF masteries are generally useful in most areas of the game. However, HoT masteries tend to be more specific to the HoT and LS3 maps.

3 - There are far more available mastery points than there are skills to spend them on.

4 - I strongly recommend unlocking the PoF masteries first as the PoF mastery system encompasses mounts, which are an absolutely game-changing QoL upgrade for players as well as just being plain fun to use! Of particular note in HoT are the glider and associated masteries. The glider may be used in most areas of the game, just like mounts, and has the added advantage of being usable in combat (there's even an LS3 map that converts the glider into its own weapon set with 5 skills you use from the air!). For Tyria masteries, auto loot is a big QoL upgrade you won't want to be without for long!

5 - GW2 has less structure to it than most MMOs. There's no gear treadmill, so that whole progression of raiding for better gear to do bigger raids doesn't exist here. However, the mastery system provides progression. There is also the storyline, which begins with the personal storyline, then living world season 1 (recap, it played out in real time), then LWS2, then the HoT storyline, LWS3, and PoF kicks off LWS4. Achievements, fractals, dungeons, raids, PvP, WvW, crafting including legendary crafting. The answer is that there is not much of an endgame here, but there's also not really a lack of things to do. The question is what will hold your interest? Nothing? Everything?

6 - I'm a member in a couple of small guilds where the people are friendly, but mostly just chat and do their own thing. I'd be happy to throw you an invite to one of them if you just need somewhere to go.

And finally, what to use that level 80 boost on? Well, I'm going to be honest and tell you I am 100% biased and have exclusively played this class since trying it out shortly after PoF released, but for me the answer is Mirage. It's a high damage, extremely mobile class with defenses based almost entirely on active avoidance and misdirection (e.g. evades, blocks, invulns, stealth, clones, target breaks, teleportation). I'm pretty good with it as I've been practicing for several months, but here's a sample of Mirage in action: