Ho, a magicianmart type campaign you had. A lot of things it explains.
Scrolls, you had to pen them. Meaning you had to pay for the spell costs while creating them. If you went to buy one, the cost of actually casting the spell was in addition to the cost of the scroll. Having a henchmen doing for you was not free. If anything, you had to pay him even more to keep this hence happy and loyal.
No, not really. Just careful systematic identification of the most cost-effective techniques, knowing what stuff you wanted, finding out how and where to get it, and going after it. Yes, you pay costs to cast for scrolls, but under controlled conditions where you can deal with it properly.
Druid might not be available for hire, especially for dungeon delving. NPC druids would not approach a dungeon, but a cave network I could agree. Only PCs ever went into dungeons. But I tight be doable. A caster would charge a pretty steep salary. That NPC might even requires a share in addition to his salary!
Well, that's of course all up to interpretation. There's nothing hard and fast that says a D&D/1e Druid cannot or will not enter a dungeon. Henchmen generally ALWAYS get a share, usually at 25% if you follow convention. At least in my experience though, henchmen were pretty close to a necessity if you really wanted to get anything done. But that points out how WIDE the range of play styles are in D&D.
As for magical items. Low level ones were expected to be found easily, but if you were playing with henchmen, it was expected that some the additional magical items would be donated to your henchmen. So selling these was not usually a thing that would often occur (unless you found zounds of them, them.their prices would go down asagic would not be that rare...)
Generally items were pretty expensive and unlikely to be available in 1e, D&D itself has few 'rules' on that kind of thing.
For money. Did you trained? Did you pay for your henchmen training? Money in a standard AD&D was not that plentiful. A wizard was notoriously money broke forest of his career until named level was reached. Then the building of a tower, paying for new spells (as transcribing from scrolls was not always a success) were also a money drain that was quite effective.
I've seen about zilch games where training costs were really enforced, at least in the 1e way. The LG players I've talked to inform me Gary never used any such rule. I can see why you might if you give out tons of gold and need to take it all back, perhaps.
Even spells were hard to find for an arcane caster as they had to either be found (random), bought (more money drain) or researched (even more money drain). I have seen groups putting their money into a pool so that their wizard(s) could have a spell for his new level. There were no cast at a higher level and if you had found no way to have a third level spells, then that cool new 5th level wizard would not cast any third level spells even if he was able. 1ed was a lot harder on casters.
In our games magic users regularly traded and maintained pools of basic core spells. Additionally ANY NPC caster that fell under the axe was DEFINITELY going to yield up some sort of books we could copy (the most valuable of all treasure really). As for the rules on starting spells and what you might or might not get at level advance in any of these versions of D&D, there wasn't any consistent rule. AD&D indicates there is a MINIMUM of spells known, but exactly what that refers to is not obvious (perhaps it indicates that if you've checked comprehension of every possible spell and not met that number you can reroll some?) Nobody really knows!
As I recall, our normal practice was that your mentor handed you a spell of whatever new spell level you acquired access to, random generation. That pretty much follows on the rule in the DMG on initial starting spells. As I say, generally any established party/adventuring band/guild would have SOME sort of library that could be accessed. When I was playing in a club with about 100 other people there was an organized Guild, the higher level guys set the dues as they saw fit. If you didn't like that, you could always lump it, but some of them enforced a monopoly on copying spell formulae! lol. That was only one town though.
There were/are MANY valid approaches to D&D, which is one of the positive aspects of the original game (maybe a little less prevalent in B/X and 1e, but still mostly there).