Perhaps it is assumed in your questions, but I would start with the positioning of the speakers in the room and how they interact with the room acoustics. I never got all spendy on acoustic treatment- I do use bass traps, but get a lot of mileage out of normal home furnishings including rugs, window treatments and some absorption from furnishings like sofas, pillows, etc..
As to accessories, the first thing I’d look at is your electrical power. And by that, I’m not suggesting buying a black box, but having an audit done of the power from your meter through the service panel and breakers to the lines feeding your system. Cleaning up old, corroded or iffy contacts, replacing questionable breakers, making sure your have a good connection to ground, are all things a competent electrician can handle for relatively minimal cost.
Whole house surge protection (type II) is good but not a complete solution- some use point of use (type III). I use a big Iso transformer to feed my main system which has a surge board in it, and obviates the need for Type III devices.
Mechanical isolation for a turntable is pretty critical and if you have a low mass table, you can probably get away with a wall shelf. I had to go the extra distance, given a high mass table in an old wooden house.
Wires- no one brand is going to be the "best" for all systems and some folks don’t think power cables, interconnect and speaker cables meaningfully differ. I can hear the differences. The best option(s) in my experience are to listen to the manufacturer/dealer recommendations (you can be skeptical if a dealer is promoting a particular line if only for profit) and to actually try different cables in your system once it is optimally placed within the room. That takes a little time- not fast A/B comparisons but living with the cables over time. This can obviously get complex when mixing and matching.
I’ve been pretty deliberate in my use of accessories (a/k/a "tweaks") since I’ve found that while some may bring an improvement in one area, they can potentially create downsides in other areas (I experimented with more than 1/2 dozen "footers" on the tube power supply to my phono stage, and found that some gave me more clarity at the expense of increased stridency). So, that’s the last area I’d focus on. It’s a process to optimize a system in a given room and takes time in my estimation.
