3Divi

So, where to start. Firstly I wouldn't worry too much about being infected in the first hours of play, it's only natural to get some damage in order to collect resources. When you have enought consider travelling to every place indicated by the explorer and unlocking the teleportation to those spots, it will grant you more "clean" space to expand. When mining start by collecting everything in the terrain directly underneath the safe spots, then use branch mining to get the amount of ores required to build decent tools (remember to get a smeltery asap to increase your efficency). one big problem is food in the early game, start one farm immediatly and expand it fast, so you can stop worrying about it.
Btw, the purple thing is "the infection" or "taint", The purple land is all infected and the biome is actually called "infected land". the flower simply converts biomes into the original ones, nothing more, by doing so it will make the fibrous taint despawn and clean the land.

Well, I dunno' if you still need help with this, with it being almost a month later...That's plenty of time during which you could've searched again and found them. But since this page came up on Google, and no other page had a helpful answer to this same question, here's the answer for anyone trying to Google search for it in the future. X:1613 Y:159 Z:1224

Wait, I know what you're talking about. The obelisk on eerie island is an odd one, unlike every other one it seems to spawn with a pure node in it. (Or at least the one in my world did.) Since the opening does specify that it has to be a sinister node that could be the problem.

And don't forget to read the quests. They seriously help. Especially if you read them. They have great information that can be obtained by reading. 

you will have a difficult time finding any any tech related metal
my suggestions,
 
1 get a Tinkers hammer for mining, Preferably made of low grade materials, or nether wood, you will need alot of cheap repair materials, and these materials are cheap and easily renewable. and never replace your hammer, don't lose your hammer, getting level ups require alot of exp and time.if you want your hammer to be made of better materials, replace the parts on your old one 1 peice at a time, this way you keep the exp.
2 use to the hammer to dig a stair case down to bed rock, make turns now and again so that its a spiral staircase and you keep a silverwood tree above you all the way to bedrock, this way taint doesn't grow on your stairs, its sucks dying of taint poison walking back up the stairs
3 keep several pieces of your hammers repair material with you at all time, so that when your hammer breaks you can repair it on the spot.
4 make a pick axe with a high mining level, use this only on hard to mine ores. and will help you get more mileage out of it.
5 mine the ores but get the redstone, all of it, and jam that redstone into your hammer on the tool forge/ tool station, this will speed up mining alot. you can also make travelers gloves and jam them full of redstone and it will give haste to many of your actions , mining included.
6 make a excavator, you will need to dig up alot of sand, for more than expanding your bio dome
7 use the Smeltery but upgrade to a induction smelter when you can and use the Sand plus common ore combination to double your ore but also get rich slag, then you can use the rich slag plus rare/ needed ore to Triple the ingot output of things you really want.