1. Unless you have money to burn, your ultralight tent will work. Under the picnic shelter, you can always tie your tent off to the tables if bugs or privacy are an issue.
That said, I use a 10 y old Mountain Hardware UL-2, which has a self-standing net and floor, but a fly that requires stakes - therefore, good for keeping the bugs off under a picnic shelter, but requires stakes when out in the elements.
As an aside - I've learned that especially in the mountains, a few stakes will save one from chasing their tent down the hill when the wind blows - even if they have loaded some weight inside.
2. Kickstand - see previous threads. I've never used a kickstand; I've assumed I would take it off after climbing the first hill along with all the other weight I wish I hadn't brought. Walls, curbs, big rocks, stick, and the grass are usually good resting places. If you use a kickstand, and there are those who have great arguments about their use to save time, I suggest caution. As a mechanic, I saw a lot of crushed seat stays due to fastidious tightening every time it loosened a little.
3. Locks - see previous threads. I use a lightweight Assus or Kryptonite retractable cable, which is only a meter long. The idea is to prevent walk-offs. Ride-offs are almost impossible as I use old (discontinued) Speedplay Frog pedals from my collection. A pedal that requires a cleat, like Eggbeaters adds some protection. I also make sure I leave my Garmin InReach mini in the top pannier pocket. If the bike actually disappears, it will give LE some time to find it. I agree with John about covering GPS units - though most cycling or hiking-specific models like the Etrex don't look very valuable with their 2 inch screens..., and in the big scheme of things, they're not. Wallets, knife, and flashlight that visible on the bike generally go with me. In the end, you won't want to leave your bike unsecured for too long in places that make you nervous. If I go out to eat, the bike - my companion - usually eats with me (or stays in a motel room).
Also, if you're in the mountains in big bear country, you might want to keep some distance between yourself and the bicycle, in case a bruin feels the need to sniff around those panniers that recently carried tortillas, peanut butter, and honey.... Although I've occasionally had the urge to take my bike into the tent and out of the rain or snow, I've never had the urge to lock it to my tent..., and especially now that I am running ultralight nylon, I try to keep my bike, with all it's weight and sharp parts, well away from the tent.
4. My panniers are ziplocked to my rack. They don't come off, and I don't worry about what is left in them at night. Small packing bags with my electronics, computer, phone, battery brick, etc., usually join me in the tent where I put my feet up to recover, while reading and taking care of business and communication. Folks don't generally steal, and they certainly don't lust after bicycle tools and small, extra parts.
5. I think your pannier set up will work fine. If you keep your heavy tools and electronics and maybe an extra water bottle in the handlebar bag, your steering should be fine. Personally, I usually run only small rear panniers and a small handlebar bag for everything I need for the road. If you need more, grab a Revelate Tangle (top tube partial frame pack) or equivalent. When off-road with some desert conditions (I just finished the GDMBR), I add a full frame bag to centralize weight with tools, food, and a large water bladder, and drop the handlebar bag down to a well-secured portage rack. I have never used front panniers..., yet. I have, however, occasionally used a heftier rear wheel and tire than in the front. (Think about how we load our motorcycles - keeping the weight in the rear over a bigger tire - so that the steering in front remains light....)
All that said about loading or even overloading the rear wheel, one of the popular multi-day racing set-ups on the mountain bikes is front panniers or heavy attachment to the handlebars, a frame bag, and barely nothing on the rear - usually a only a minimal down comforter and coat in the seat bag. These folks then run a larger tire up front than they do in the rear - especially with the older frames that don't take 2.5 inch tires. As most of these young riders can kick my ass, I can't find any flaw in their set-up. It certainly keeps the front from becoming too light and wheelieing up the steep hills.
In sum: No hard rules other than to avoid wheelies while touring up hill (I mean unless you're really good at it). Try to keep the weight central and low and have respect for the load you ask your wheels and tires to carry.
I've attached a photo of my overloaded (50 pounds of tools, parts, gear, and water) Karate Monkey at the top of Hoosier Pass - on the Trans-Am. (Yes, that's a spare tire under the down tube....) Hopefully you'll have a similar photo at some point to share when asked how you carried your kit.
