I'm not entirely sure I follow all of the questions, but I'll try to hit them all. If I miss any, Sunshine Daydream maintains amazingly good crafting guides for all facets of the crafting games.

Trade skill line levels

The only helpful point based on your post is to say that you may level your trade skills to fifty at any time. The levels of the skill lines themselves don't change drops or writs. They only dictate how many skill points you can spend in passives, which is what determines drops and writs. So go as fast or slow as you like.

Node drops

You didn't ask, but this might help. The type of materials your character picks up from a node is a mix between their character level and how many points you spend in the first passive of that skill. In other words, if your character is at a level where they can wear dwarven metal armor, but they can only make up to steel, nodes will be a mix of drwarven and steel.

Writs

The writs you receive, and therefore what you're asked to make and here you drop them, is determined entirely by the points spent in the first passive of the skill line. At lowest rank, they all drop in the starter city. When you spend a point in that first passive, they will require the next level of materials and drop in zone 2...one of the capital cities.

Note that there are not an equal number of ranks for all skill lines. Alchemy only has 8, and provisioning only has 6. It's been a loooooong time since I've done lower level writs and paid attention to where they drop. I could be wrong here, but I think this is accurate - I believe that all skill lines go through zones 1-5 then move to Hollow City on a non-vet character or Craglorn for a vet character. That's to say that if you're doing Cloth writs, ranks 6...7....8...9...10 will all drop in the same place.

Writ rewards

In general, ignore the numbering system on the reward packages. These are based on the rank in the first passive, so alchemy and provision won't match up wth the other skills. The numbers don't mean anything, other than the fact that you have a shot at better rewards (mostly gold mats) the higher the writ level. And you ONLY get master crafting writs from top level writs.

And the only passive to be concerned about is the first in each line, that allows making stronger stuff. None of the other passives affect your writs at all. Only invest in them if you need the perks they provide.

Hirelings

These can provide valuable materials. If you don't have ESO plus and a craft bag this can be an inventory management problem. But either way the mats can be helpful for crafters.

When I didn't have a craft bag I still used hirelings, then had an enchanting alt, alechemy/provision alt, and equipment alt. These characters picked up the appropriate emails every 3-4 days and management wasn't so bad. In order of value, I'd say it goes smith, cloth, wood, enchanting, provision.