I am wondering how feasible either a solo or two-man attempt on the main trail would be during the middle of this December (17th/18th-ish)?? I am fully aware weather will dictate many things, but I am just wondering people's thoughts.
I am an "intermediate level" mountaineer/climber with numerous climbs in and out of the US, up to 6000m. I am from Minnesota and have plenty of cold weather camping time.
Yes climbing Mt. Whitney on those dates in December is feasible. As you point out some of what you bring and how your prepare is going to be dictated by what our weather does between now and then.
Would one use stiff-shank mountaineering boots for the whole trail (ie: Nepal Evo equivalents)? Could you get away with micro-spikes on hiking boots or are crampons and an axe necessary?
It could be either. I'm a fan of using a bigger boot for a couple reasons: (1) I know that regardless of conditions my footwear will be fine, and (2) my feet get colder easier than most. I've been a Lowa boot guy for years now and would choose either the Lowa Weisshorn or Latok. You can look at those models and find your equivalent if you need another brand.
If we don't get much more new snow between now and mid December chances are the trail will be mostly dry until Trail Camp. Light hikers and micro spikes would probably be enough if that was the case. Again, it's difficult to say as of now so you should prepare for both and wait and see.
If we get more snow the slope above Trail Camp called the 97 Switchbacks is north facing and will hold on to snow because it doesn't get much sun. I'd have an ice axe and crampons. Even if we don't receive any snow and you decided to go with micro spikes I'd still bring an ice axe. It's a steep slope with a couple icy spots. With a good trail and no ice trekking poles are sufficient.
What are most people bringing up in terms of equipment and sleeping bag ratings?
I'd bring a sleeping bag rated to 0 degrees Fahrenheit. Some would argue bringing a warmer bag while others would bring something lighter and wear enough clothes to sleep in. Inside a tent a 0 degree bag should be fine.
Is there a gear rental outfitter nearby if I bring a friend?
In Lone Pine you'll be limited to what you can rent. In Bishop there are two shops: Mammoth Gear Exchange and Eastside Sports who rent a few things plus our guide service Sierra Mountaineering International Inc offers rentals on some items. Where you rent gear will depend on what you need.
Would I need a shovel and avy beacon?
Yes bring a shovel. If we get a lot of snow I'd highly recommend a beacon and probe plus the knowledge on how to use them. The shovel will be useful for lots of things including leveling a tent platform, gathering snow for water, building walls around your tent, making a kitchen, etc. The avalanche gear would be a great idea if we get some good snow between now and then.
Any recommended plan for an itinerary and places to camp?
If there's snow your progress will be significantly slowed versus a summer dry trail. Figure on a day to Outpost Camp, another day to Trail Camp, a summit day, and a descent day. You also may need to start below the summer parking lot at Whitney Portal if snow prevents you from driving the entire way.