The free trial version ends when you buy the full game. (It also has a lot of limitations that go away when you buy the game, so is really only suited to people trying to decide if they're even interested in the game enough to buy it. If you're sure you're going to want the game, it's better to buy it up front and start off with the full thing that gives you access to chat, trading, forming parties, joining an FC, etc, which are all either limited or blocked entirely in the free trial.)
But buying the base game should have automatically given you a 30 day subscription included in the price of purchase, so it should have taken a month from registering the game before you needed to pay for subscription time.
Maybe for some other MMOs that might be the case, but not here. People who come here expecting everything to be at end game (based on experiences in other games) tend to be disappointed when they get there and realize most of the good content is in the stuff they raced past trying to reach something else. Explore. Try out everything. Enjoy the journey, it's the best part.
The story itself in ARR would be pretty good, except that it has some pacing issues which turn an otherwise good story into sporadic good segments interspersed among other stuff. There's places where it has lots of fluff content that does little to advance the story, and other places where it has long stretches of story exposition without enough activity.
The main scenario quests can be distinguished from others by the type of quest icon. (Main story has a flaming ring around the icon where the icons for other quests just have a Q, or in the case of sidequests that unlock features, a Q with a plus sign in the corner.) Even the plain sidequests can sometimes have a story to them, though, or fill in some background lore. There will be more side stories with a substantial story to them at the levels that have been endgame at some point than there are during the leveling ranges, though.
Saddlebags certainly help, but retainers are the bigger cure for inventory issues. Your saddlebags can hold 70 items, whereas your retainers can hold 175 each, and you get at least two for free (and can have more if you're willing to raise your subscription cost for it). Retainers are also unlocked earlier in the story than your chocobo is, as you can hire retainers any time after you join the Scions of the Seventh Dawn in a level 17 main scenario quest. That's the threshold I usually suggest getting to before getting too deep into crafting and gathering, though you can certainly unlock them and try it out a little before then.
Until getting retainers, I'd limit gathering to only those items you need for a craft you're planning to do right away or that you need for a quest, and limit crafting to items you want for your own use or things you need to turn in for a quest or levequest. The recommendations to make and gather one of everything for the first-time XP are fine once you have retainers to hold what you'll want later and sell off what you don't want, but not when you're keeping the resulting item clutter in your main inventory.
This rumor started way back when ARR was first released, based on a badly worded help screen, and has persisted ever since, but it's wrong. The bonus is and always has been a fixed amount, and is not based on the difference in your levels. It's 100% up until you reach a certain threshold (on the class you're leveling at the moment, not on your highest class), and then 50% after that. That threshold used to be at level 60, but I'm assuming it changed to 70 when ShadowBringers came out (just like it changed from 50 to 60 when StormBlood came out). I haven't actually checked that detail, though.
With gathering quests, and occasionally others, the next objective is actually turning the items in, and you're on your own for where to find them. Many items can be gathered in multiple locations, but your gathering log should tell you where they are, with the specific area (Treespeak in this case) listed under a heading for the region (North Shroud). If you opened your map while there at the Botanist guild, you'd have seen the gate to the North Shroud is just south of it, between the BTN guild and the CNJ guild, and once you get to the North Shroud you can open your map to see that you're in Treespeak, as it's the first area just past the gate. IIRC, though, you might have to look around a bit for the right trees to harvest from, as there are multiple groups of them and only some yield the items you're looking for. (Though when you find the right group of trees, all trees in that group yield the same items.)
Having come from an MMO that did let us play solo all the way to endgame if we wanted to, I remember this taking me by surprise when I first started and hit that mandatory run of Sastasha. It didn't take long before I came to enjoy it, though. We seem for the most part to have quite a friendly playerbase, and being given a reason to run things with others got me to do so a lot more than I would have on my own if it had been optional.
I agree. That help tip only pops up once, when you're likely to be too busy to read it, and the most obvious place to look any other time is the skill tooltips that just say the name of the buf they add to or remove without saying what it does. Managing the Astral Fire and Umbral Ice buffs is so central to THM/BLM combat that it really needs to be described in the most obvious location where people can find it — the skill tooltips.