its definitely hard, and you don't earn enough scrap to really upgrade your ship imo. There's just way too much stuff to upgrade and not enough scrap. even on easy. I never have enough to buy anything more than a few fuel or repairs when I reach a store.
I saw 1 "guide" mention to hang around each sector and go to different nodes, but the rebels show up too quick and you can't really get to do much.
Yes, you want to maximize each sector. Ideally you want to jump out of the sector right as the rebels reach the jump point. Occasionally (probably once per playthrough) I'll be caught by the rebels at the jump point. It can be worth it, if it meant hitting a good store or getting some good scrap.
I always try to keep 100+ scrap on hand just in case I run into a store. I never upgrade unless I've saved up 300+ or so, and I do a bunch at once (power+shields, etc.). Another thing is that you can count on a decent assortment of various parts (drone schematics, various beam weapons, etc.) from your defeated enemies that you can sell to stores.
You can go a whole playthrough and never find your preferred weapons at a store. (My preferred is to have 2x Burst Laser II's + 1 ion cannon.) So you have to be flexible if you don't find what you want. I have come to rely pretty heavily on the Teleporter. Get a Teleporter early on, and a Bug + Rock crewmember. If you capture a ship by killing all of the crew instead of blowing it up, you get extra scrap.
Basically it's all about augmenting early on. If you can get the 15% Extra Scrap augmentation early, it's party time. And the Long-Range Sensors are huge in finding which sectors to jump to, in order to fight another ship so you can earn scrap. I will get those as early as I can. Teleporter as well. I usually don't upgrade my shields and until the 2nd or 3rd sector. Getting extra crew early on is very helpful too, so they get the chance to get experience. (Want to keep 1 person each at Helm, Engines, Weapons, and Shields the entire game, so that they can level-up at that position and get the cooldown bonuses.) So yeah, I front-load my expenditures heavily. Don't perform any "homegrown" upgrades in the first 2 sectors or so; save all your money for buying stuff from stores, since your extra equipment will determine the evolution of your ship.
And the Teleporter is crucial in the final battle. The main laser weapon has to be disabled in each of the 3 encounters, and the quickest way to do it is to teleport 2 crew members into that compartment and bash on it. In the first encounter, you have to kill the crewman first, but he doesn't come back in the later encounters, so it goes quicker. That weapon is the one that does the most damage. If you have 2 bug crew then send one to disable the laser weapon, and 1 to disable the missile weapon. Then when the boss does its "power surge" it is largely impotent and can't penetrate your shields.
I almost never use Drones. Too much power system suckage for limited utility. Now that I have the Federation Flagship, I use it pretty much exclusively. Its built-in beam weapon is killer! Upgraded fully (using 4 power) it recharges in 20 seconds. It penetrates all shields and does 1 damage per room hit. It also starts with 4 crew members: 1 Human, 1 Engi, 1 Bug, 1 Stone. This is a killer mix, I put the stone in the weapons room where he can take lots of damage and also defend pretty well against boarding attacks. Engi in the engine room, human at the helm. Bug goes in the transporter room once I get it. Also try to find at least one more Engi and another Bug. The Engi are invaluable for quick repairs, and the Bugs just slash through enemy crewmembers like crazy.