Take it slow and steady in my opinion, don't rush, espically as you've chosen a massive monster of a modpack. As for starting mods here are a few I'd recommend, in no particular order:I'm starting into FTB (I've choosen Infinity), How do I do to not get lost? Any good tutorial recommended?
-Botania:
Pros: The Soujoner's Sash is pretty early game botania, and allows you to get around quicker. The Exoflame can let you power a furnace with Mana (it even makes the furnace slightly quicker), and the Agricarnation can speed up crop growth. Manasteel armor, assuming you carry around a mana tablet with mana on it (or the ring versions) is a very effective early game armor. It's a very fun mod (imo)
Cons: It can be fairly slow to start off, as Dayblooms and Nightshades are fairly slow at making mana. This hurdle is largely overcome when you gain access to Mana and Runes. It also doesn't provide a way to increase the value of the ore you mine.
-Tinker's construct:
Pros: Very Potent and Customizable Tools. A fairly early game way to double ores. Is fairly easy to do alongside another mod.
Cons: It only really offers tools. The smeltery requires both Clay to make, and Lava to fuel, both of which can be a little difficult to get alot of in the early game.
-Thermal Expansion + Thermal Dynamics or Ender IO
(Yes I bundle these together more due to them being very similar in Pros and Cons. If starting out I'd likely stick to one side or the other, early game they pretty much identical aside from how you get the ducts/Conduits. Thermal Expansion's machines, fully upgraded, tend to be faster than Ender IOs, but Ender IO doesn't ask you to exchange side products for speed. Alloys are generally also easier to make with the Ender IO Alloy Smelter rather than TE's natrual method for it's own alloys (Predominatly Signalium and Enderium here.))
Pros: Very Plug and Playable. Fairly simple Ore Doubling. Upgradeable machines. A vast array of options to generate power.
Cons: (Ender IO only: Conduits need power to make, meaning you either need to place the alloy smeltery next to power gen temporairly, or use another power transport.) Can take time to find the materials needed.