I didn't start kegging till about batch 35ish. Resisted kegging for as long as I could. Kinda glad I did, because I could concentrate on brewing. Took plenty of time to plan out my keezer build.
I second the cereal killer mill. I've put hundreds of pounds of grain thru mine, no issues. You can get it delivered for $100.
https://www.homebrewing.org/Cereal-Killer-Grain-Mill_p_2310.html
Again, this totally depends on the beer. I've had beers that were not very good as soon as they were carbed. After a couple/few months on the shelf they become a totally different beer.
Depends on the style of the beer. Darker beers tend to get better over time. When I bottled I always kept a few in the fridge, and the rest were in the basement on a shelf, no matter what the style.
Get good faucets, go with Perlicks or Intertap. No reason for them to go "skunky." I'll often go a week or two between pours of a beer and no issues.
Here is my recent built, if you're looking for some ideas...
Mine is about as simple as it gets. There is an eyehook in the patio roof where the bag hoist gets attached. I do have a cooler full of ice and water with a pump to run the wort chiller.
I put mine on the hump side. No kegs on the hump, so they are out of the way. It's your build, you can put them anywhere you like. Just keep them close so you don't have to buy a huge drip tray.
Simple control panel, then you need some sort of element. That element gets mounted into the pot? Got to have the wiring to your panel, there's a 220 circuit. A lot more initial setup with electric.