Don't have much time in a g1000, only about 5 hours from a couple years ago. My company purchased two brand new caravans with the g1000 suite. Any tips for a guy transitioning from steam gauges to glass?

I recommend to go to a flight school and sit with a Cessna 172 G-1000 powered up with a GPU and learn it. Pay a flight instructor that can help but make sure they know the system. AHARS, Magnetometer in the left wing, Air Data Computer, Engine/Airframe Unit and the faults. You wont get enough time to learn it at flight safety. Also, G-1000 means you get the TKS Systems versus boots. There is also that to consider...

You have any experience with the 430/530? If so, it should be an easy transition.

When I transition folks to the G1000, I tell them to expect around 5 hrs before you are 'operationally dangerous.' Most Pro Pilots will have it down and very comfortable at 10 hrs or less, and could easily teach others by then.

Just remember the whole thing is based off the 430/530, it's separating those functions from all the bonus items. You will love the autopilot too btw. FLC=IAS btw on the AP.

I am very familiar with the 530/430 stack. Company will have to provide training, otherwise I might get an instructor. I have heard the autopilot is incredible. I am very much so looking forward to learning the g1000.

This is correct, navdata remains viewable/usable after it is no longer valid. BUT, if you Have chart data, it is no longer viewable shortly after expiration. So, navdata stays, chart data goes.

Having never used a G1000 with this software version, I couldn't tell you. I would be surprised however, if holds weren't a menu item in the flight plan page. I would assume while in the flight plan you could highlight the fix, press menu, and "hold" would be an option. Just a guess though.

So, is it possible to add a G1000 after market, on a old 1960'S Cessna 210, for example?

Yes you certainly can!

Adding Airways To A Flight Plan - Garmin G1000:Socata User Manual [Page 217]

Adding an airway to a flight plan: 1) Press the FPL Key. 2) Press the FMS Knob to activate the cursor (not required on the PFD). 3) Turn the large FMS Knob to highlight the waypoint after the desired airway entry point. If this waypoint is not a valid airway entry point, a valid entry point should be entered at this time 4) Turn the small FMS Knob one click clockwise and select the LD AIRWY Softkey, or press the MENU Key andselect "Load Airway". The Select Airway Page is displayed. The LD AIRWY Softkey or the "Load Airway" menuitem is available only when a valid airway entry waypoint has been chosen (the waypoint ahead of the cursorposition).5) Turn the FMS Knob to select the desired airway from the list, and press the ENT Key. Low altitude airways areshown first in the list, followed by "all" altitude airways, and then high altitude airways.6) Turn the FMS Knob to select the desired airway exit point from the list, and press the ENT Key. 'LOAD?' ishighlighted.7) Press the ENT Key. The system returns to editing the flight plan with the new airway inserted.

The G1000 is not available for aftermarket installation. The closest you'll get is a G600 which is a combination split screen PFD/MFD. There are a lot of options though for aftermarket glass retrofits into older aircraft.