You downloaded it - nice Yeah it does take quite a bit of RAM to run, I thought it was suggested 4Gb but always good to give as much as posisble.
Watch out for Draconium reactors, they explode! To be honest though the whole Draconium evolution is late mid / end game so I wouldn't worry about that to begin with.
A few general tips to start with is when searching the crafting menu if you type @ and the start of the mod name you will get all of that mod. So @Themral gives you all Thermal Expansion, @Tinkers will give you tinkers construct etc. Another general tip is make a sleeping bag. You still need a bed to set your spawn as in vanilla but a sleeping bag allows you to sleep anywhere and won't reset your spawn should you die. Very handy to have if you're out and about so you don't always need to go home to pass the night. Finally, on the items on the right side of the screen that you can click on to craft with, if you left click it will tell you how to craft it, right click will tell recipes it is used in.
I'd say the first 2 mods that are worth getting in to is Aroma1997 Mining world - You go through a portal like a nether portal but it takes you to a flat mining world which you can dig up to your hearts content without ruining your normal world. The second is Tinkers Construct - it takes a little resource gathering to build the smeltery but it comes with the benefit of early game albiet manual ore doubling. The biggest advantage is the tools it allows you to build - picks, shovels, axes etc. that can be upgraded and modified. The perks each material has when making the tool or in modifying it you will need to look up as there's too many to list here I'd also say look in to setting up a refined storage system, it's my preferred storage system as it integrates a crafting grid and is easy to us, make things and see everything in one place. Though know, a Refined storage system isn't cheap to make so you'll need a little mining under your belt first.
The refined storage system uses power though (mostly called RF in this mod pack) so before you can build it you'll need some of power generation. How you generate power is up to you, there's a number of generators that run on coal, lava, food or other fuel sources through to solar panels, extreme reactors (which won't explode so no worries there) to nether star generators or Draconium reactors (which can explode!) etc.
After that though it is up to you, I think it's pretty clear I like the automation side of things so I go off down that route but there's no reason you have to so the choice is yours.
Any questions though just ask and I'll try to answer them as best I can