Couple of questions about my new "old" Performer

I got this off a guy from Craigslist, it's the old stainless steel kind. I paid $150. It was never used, still had the plastic on the stainless steel top. I apologize in advance, as I know there are several threads on this topic and I have searched and read them but would like to confirm my thinking based on those threads. Grill comes with the 5 pound cylinder. But this does not have the new type threads, so I presume it can't be re-filled. (Interestingly, it is a virgin tank that has never experienced a fill up). What are my options?
1. I see there's a part called a reserve-adapter, $20, that would connect to the existing regulator, and would allow me to plug in a 1 pound disposable tank. Apparently these are good to have around if your 20 pound tank runs out during a cook, but it seems like it would make my grill usable with a 1 pound tank like the new ones. Fortunately, there's a little switch on the regulator that can shut off the gas flow. (I've also seen fill-adapters that let you re-fill the 1 pound tanks from your 20 pound tank)
2. I can hook up the existing regulator to one of my 20 pound tanks. A good option, but it seems like overkill to have a 20 pound tank for charcoal starter. And it doesn't really fit on the shelf underneath.
3. I could buy a new 5 pound tank. I hear they are about $50 from Weber. That's a lot. I can't seem to find anywhere else that sells them.
4. Is there a re-fill adapter or nozzle that would allow me to re-fill the old 5 pound tank from my 20 pound tank?

What year is the P? (Check the code on the bottom of the lid vent here, or look for the small white sticker usually on the bottom of the control panel--where the gas valve and ignitor button is). If it is less than 10-12 years old, it probably has the OPD valve, and therefore can be refilled by any propane refiller.

One thread poster stated that Cabela's sells the 5 lb tanks, so check w/ a local large hunting/fishing supply store.

The 20 lb tank will do a lot of starts. The 5 lber is rated at approx 150 starts.

Sorry, I don't know anything about refilling a 5 lb from a 20 lb tank.

Its not the threads on the tank but the OPD valve thats the issue. You'll have to replace the tank and I've seen them for around $35-$45 at sporting goods stores. Harbor Freight has the refill adaptors for the disposable propane tanks (New Performer) and Mr Heater sells a "Steak Saver" adaptor that you could mod, but the investment in a new tank would be the way to go.

There is a large round "o" squarely between two of the vent holes on the grill cover. If that's the right code, looks like a 1992. I know the seller had this sitting around a bit (he never fired this grill), but I'd be stunned if it's 16 years old! However, it has a 5-star propane tank valve, and the new ones are the triangular ones.