I’ll do mine based on your suggestions:
Oxygenating - very very important, but unless you are making HUGE alcohol beers, using your store bought mash paddle and splashing the thing around in the for 2-3 minutes is sufficient…IF you are pitching enough yeast (not just a smack pack/vial)
Filtering - not important…maybe for clarity, but there are other ways to get that
Using a wort Chiller- this helps your ‘beer made : time spent brewing’ ratio, and some say it can help reduce DMS (cooked corn/cabbage flavor), BUT I have made some great brews with no-chill/partial chill. An immersion chiller is a good pick up. I would almost advise just buying one as the price of copper makes building one (which I did) about cost-neutral, especially when you factor in the value of your time
Temperatures - HUGE. huge, huge, huge. $100 Johnson temp controller, and used chest freezer on craigs list. Best $150 I’ve spent on any brew gear.
Hop additions - not sure what you are referring to, but as long as you follow a GOOD recipe, this shouldn’t be an issue. Pick up or borrow Brewing Classic Styles.
etc.
Do you use brewing software? Try out one of them (BeerTools, etc.). You can also use Hopunions site for free. Amongst many other things, this will allow you to keep lots of notes (ie gravity was 1.052 instead of 1.058, forgot to add campden tablet, etc.). Its so easy to forget.
I would also suggest trying to brew with an experienced brewer. I had 15-20 brews under my belt, and brewing with some other guys helped me realize some things I had been doing wrong all along (ie leaving the boil kettle lid on! Though this didn’t seem to have much of an effect (some say it will cause excess levels of DMS))
Make yeast starters too. Every time, even for 1.050-.060-level beers. Dangers of overpitching are far more minimal than those of underpitching.
FINALLY (and this was my hardest lesson to learn): PATIENCE. I primary for 2-3 weeks MINIMUM now. No secondary. As above, the dangers of oxygenation/infection with transferring far outweigh the dangers of leaving a beer in primary for 3, 4, 5, 8 weeks.
As Gordon Strong says, its all about learning your system, and how to minimize ‘stuff you don’t want’ and maximize ‘stuff you do want’.