1.) Stick with FL sizing and add mandrel expanding the necks.
2.) Bump the shoulders .001-.003 but check the brass in your chamber to make sure it closes without resistance before settling on a particular bump. With the dies properly adjusted you'll get the correct shoulder bump. Use a headspace comparator to find these numbers.
3.) Neck tension gets complicated and seems to be never ending. I would start by using the mandrel die to expand your necks after FL sizing and using premium brass to start.
4.) Your bullets most likely pulled harder because of cold welding of the necks. The copper jacket and brass case react to one another and will begin to corrode. There's a technical term and description for this, but essentially they weld together. I've seen it happen. The only way to stop it is dry lube in the case necks or don't leave your ammo sit for more than a month or so. I'm currently in the process of testing moly applied as a dry lube inside my case necks. I learned this from reading and watching videos on Lou Murdica's process.
As far as other techniques. The rabbit hole is endless. I honestly am starting to take some things less seriously and focus more on myself as a shooter and making sure I'm consistent day in and day out. Having your powder weighed to the kernel or your ammunition have zero runout will not help you as a shooter, it won't hurt either, until you're able to shoot good enough to recognize those problems. However, there's the psychological effect in that if you think a certain process/processes make you better and give you confidence, then keep doing that!
I like to advise people to add simple things to their process that won't cost an extraordinary amount, but will help for sure. The number one thing is a mandrel die. Sinclair sells them for like $30 and you can buy the individual mandrels from them or others for roughly $15 each for stainless and around $50 each for carbide. The stainless is great but you have to lube the inside of the case necks to prevent gauling. I also would get a set of headspace and bullet comparators as well. I also like to run a nylon brush inside my case necks before charging the cases. It has been shown by reloaders much more skilled than me that it helps. Other than that, I would continue doing what you're doing until you plateau or want to gain more consistency and/or precision. Learn everything inside and out then level up.
If you have deep pockets you can jump right into the most expensive and high tech equipment there is. You may never be able to take full advantage of it, but you'll never have to question your equipment. There's many paths to go down. I prefer to do the most I can with the best equipment I can afford. There's some really good stuff out there that's relatively affordable that can improve your ammo, save you time, and make reloading that much more enjoyable.
Sorry for being long winded. If you want me to explain more on what I use and what I recommend, or to explain more let me know. I can post it here in the thread or PM you if you're interested.