I've been using the same power armor I found since I first used it. Built it up with some pretty nice components. I have around 75 cores.
At your settlements, you can set up stores (after unlocking certain perks). Your weapons dealer (whomever you assign to run the weapons store) will start selling Fusion Cores. They're pretty expensive, but if you save up plenty of bottle caps, you won't have any problems building up a stock of Fusion Cores to run your power armor. You can also unlock perks (or abilities) that stretch out the duration of said Fusion Cores.
If you want to run power armor throughout the campaign, you'll need to build up your science and armoring perks so you can create higher quality uses and pieces for your power armor. With the right mix and match of abilities for your armor, you'll have a pretty durable piece of gear.
Make sure, at your settlements, you have a Power Armor repair station set up. Keep a good stock of steel (usually broken down from weapons and from junk found around the wasteland) so you can keep repairing your Power Armor after a mission when you return to whatever you've determined your base to be. Setting up supply lines between multiple settlements allows you to use resources at one settlement as if it was stocked with the supplies at a better endowed settlement.
Also, be sure to cook up some good foods that have varying effects. Some foods will allow you to add 25 pounds carrying capacity for a short time. Others will allow you to resist a cetain amount of rads for a while, do extra damage, breathe underwater for 30 mins, all sorts of cool effects, in addition to restoring varying amounts of HP.
Certain complete paint jobs on your power armor endows is with other abilities. I believe the paint job I put on my power armor upped my carrying strength. My two leg armors also increase its carrying strength. (Or maybe its the arms, I forget). I also have two mods for the torso armor, Stealth Boy (which kicks in when you kneel in power armor, as long as you don't move) and Jet Pack, which can enable you to reach some places that were difficult to reach without it, or clear some pretty big gaps, as long as you have the Action Points to make it. Jump Jets use AP. When you run out of AP, you have to wait to get some AP back to use it again.
You can only switch out mods at a Power Armor station, so its not like you can do it on the fly.
When it comes to weapons, I have a few criteria to help me decide which weapons I wanna sell, which I wanna mod, and which I wanna store, or which I wanna scrap.
When it comes to selling, make sure you can outfit yourself with clothes that boost your CHR (Charisma) ability.
Resale value: If the resale value of a weapon is at least 90 caps, I'll consider selling it to a vendor. Otherwise, it's a candidate for scrapping.
Damage Value: If it already has a high damage value, then I'll consider modding it, if I have the resources. One of my big favorites to mod a weapon with is the suppressor. Another is the long range recon scope, generally handy for sniper rifles. With the recon scope, you can tag your targets, and keep track of them, even when not aiming down scope. NOTE: Mods can add weight to your weapons and armor, so choose judiciously.
Legendary weapons and armor cannot be scrapped, but can be sold, stored, or modded. You can also rename your weapons and armor at the appropriate work stations.
Ugh....there's so much more, but I have to go sing. Have fun!
I'm playing it on Easy and I'm still getting my ass kicked. I'm running around doing side quests just to grind up.
I did read that basically the NW corner is lowest level and goes higher as you head SE. So I'm afraid to do these early story missions that are already on that half of the map.
