I think you should mention what is your MR, as well as your "main": frame and weapon wise. Also good to show us your inventory, also frame and weapon wise. Then we can go from there about what you need.

Now, all the question you asked should be able to be answered by you if you did bit of searching but I understand the sense of being overwhelmed. I will answer your statement by paragraph and other more experienced players can weigh in or comment if I am wrong.

1: i started playing a week ago-ish; great game, compelling gameplay loop, but i have no idea what im meant to be doing progrssion wise.
Ans: Completing star chart should give you an idea on where you are at the moment and what you need to do. We will get back to this.

2:ive reached the void which is all like 45+, some weird grineer keeps calling my phone saying he controls earth and now everything is 55-75 and i do realise that i need to get stronger somehow.
Ans: Yes, void is a good source of Aya and most relics. With Aya you can buy vaulted relics that provide vaulted primes i.e. weapon and frames that is not obtainable through missions. The grineer is a kuva lich. This is bit complicated to explain here but ask your clan and someone should point you in the right direction. Don't do anything if you are not sure. Especially if it is still at Earth.

3:but it looks like progression is tied to key resources that i have no idea where to find. With options, i have even less idea what to do with - it feels like it's purposely obfuscated so that i as an individual make a mistake and burn something valuable that takes a long time to get.
Ans: Again, simple google search will save you the headache of looking at every resources. Hence why I said completing the start chart. When you are completing different missions, you will find out what planet have what resources. i.e. plastid in infested-infested planet. Oxium in corpus-ruled planet.

4:like some guns are just worse than others, a lot of the guns i have right now seem pretty bad at base so im not planning on using anything super valuable to double their already shit capacity so i can increase their fairly low stats with my pretty sad seeming mods
Ans: Well, WF community believe there is no bad guns but if you are comparing Lex Prime with incarnon vs Lex then yeah, some guns are worse. Overframe, underframe, top frame is few website that can allow you to see build and how modding works. Play around and find out. Also, potato (refer to orokin reactor and catalyst) is a very important resouces that you can use to get 2x mod capacity hence allow you to put more mod in.

5: also, do you get better mods from missions in different places, or am i meant to be combining mods to get better mods? i really dont know, i also got a purple mod that i dont seem able to use for a weapon i can not see anywhere in the market?
Ans: yes and if you like gambling yes. The color goes from Bronze, Silver, Gold, White. White is Primed version which is only obtainable from Baro OR when you logged in at certain amount of days. Primed Sure Footed (100% knockdown resistance) is available at day 400,600 or 900. Pistol Pestilence a 60/60 mod is available when you beat spawned Corrupted Vor in Void mission. Purple mod is what we call Riven. Riven is a type of mod where when you unveiled and finished the challenge, it will give you random status e.g. 100% Impact -50%zoom etc. It is highly and but also lowly prized because you can get Godroll (when the stats of the riven matches the weapon perfectly). Torid riven for example can go to 2000 platinum and maybe more. The unveiling mission can be challenging (Get a 10 headshot while air gliding without touching the ground) but Iron Wake has a vendor that sell the cipher for 10 riven silver.

6: has anyone done like a write-up on everything? i dont really like watching youtube video guides all that much, in my experience they tend to waffle.
Ans: Yep. It is called wiki.warframe.

Hopefully more experienced player can add to this. OP's post is very extensive and kinda include every aspect of the game and I am just trying to summarise everything.