Everything under Dropsuit Upgrades. Just leave out the Equipment if you don't use it.

I left reps and rechargers/energizers at level 3 because I think they were good enough.

Electronics and Engineering at 4 because near a million SP for the same increase in fittings as before was, IMO, a wasteful SP sink. I'm content with my current fitting capacity.

I do agree that I specced into too many ADV suits and weapons, which is what I'll use a respec for.

They're not "more important". They're "equally important".

My friend, who had max cores, and was working on electronics, engineering, and hacking stopped working on them when reaching 3 because he grew tired of facing protos and ADV with only the first 4 starter fits he had available.

He said, "going from MLT to STD really made a great difference". He also complained about matchmaking, but that's a story for another thread.

I would advise getting the initial cores to 5, then getting STD equipment so that you have a much better chance at everything rather than sticking with MLT.

In my opinion what every newbie should understand is that the skills that work in the background are more important then the equipment that you can stick onto your suit. There are alot of skills in the game that help you to fit more/better stuff on a lower grade suit or give you a universal HP boost. So lets begin what a newbie should get to lvl5 first:

-Dropsuit core upgrades, this skill increases the PG and CPU up to 5%. Skill cost: 621.840 SP
-Dropsuit Electronics increases the CPU of all suits up to 25%. Skill cost: 1.554.600 SP
-Dropsuit Engineering increases the PG of all suits up to 25%. Skill cost: 1.554.600 SP
total SP cost: 3.731.040 SP

These 3 skills have the highest priority in the whole game and should be specced out first cause you have a insane fitting advantage once you are done with that. Next step is to increase your dropsuits base shield/armor HP and access to modules increasing HP. The next step depends if you prefer to armor tank with amarr/gallente suits or shield tank with caldari/minmatarr suits.

-Dropsuit shield upgrades increase the base shield HP of any suit by 25%. On a Cal. assault that is 68 additional HP.
Skill cost: 621.840 SP
-Shield regulation make your shield regulators up to 10% better and gives access to that module too. (lowers shield recharge delay)
Skill cost: 932.760 SP
-Shield extension makes your shield extenders up to 10% better and gives access to shield extenders (HP module)
Skill cost: 932.760 SP
-Shieldrecharge makes your shield rechargers+energizers up to 15% better (HP regen module).
Skill cost: 932.760 SP

-Dropsuit armor upgrades increase the base armor HP up to 25%. On a amarr assault that 78 additional HP.
Skill cost: 621.840 SP
-Dropsuit armor plating makes your armor plates up to 10% better and gives access to sayd module.
Skill cost: 932.760 SP
-Armor repair systems makes your dropsuit armor repair module up to 25% better.
Skill cost: 932.760 SP

Those skills help you to fit your suits significantly better. However you should note is that picking armor suits is less skill intensive then shields due to the fact that shields have 1 more skill to spec out then armor. After youve specced out the PG+CPU skills it depends what suit you want to use. The philosophy of each race is rather simple:

Caldari= long range combat and shield tanked suits (rather high SP cost to spec)
Gallente= short range combat and armor tanked (low SP cost to spec)
Amarr= long+short range combat who prefer to bricktank with lots of plates. (very high SP cost to spec)
Minmatarr= dual tanking+speed modules required. Short-medium range combat. (extreme high SP costs to spec)

They're not "more important". They're "equally important".

My friend, who had max cores, and was working on electronics, engineering, and hacking stopped working on them when reaching 3 because he grew tired of facing protos and ADV with only the first 4 starter fits he had available.

He said, "going from MLT to STD really made a great difference". He also complained about matchmaking, but that's a story for another thread.

I would advise getting the initial cores to 5, then getting STD equipment so that you have a much better chance at everything rather than sticking with MLT.