There's no need to remove the oil filler cap or dipstick during the drain, but it won't hurt. The PCV system will allow air to enter the crankcase to replace the displaced oil.
To avoid a mess when you remove the filter, first loosen it a quarter turn - to make sure it will come off, then puncture the highest point. Now proceed to removing the pan plug. The filter will drain, and if you give it about 10 to 15 minutes, there will be little or no oil spilled when you remove it, but cover the bottom with a rag as you spin it off.
I also lift the car on the right rear jack pad to lower the oil drain, which allows a more thorough drain.
I have a "socket" that fits over the top of the filter than makes loosening it easy with a rachet and extension, but I don't recall the size. I think I took a new Bosch 72165 filter to a parts store years ago and found the correct oil filter socket that fit snugly.
The pan capacity is approximately 6.3 quarts, but I usually just install 6.
The oil pan bolt torque is 18 lb-ft, and I recall that the hex is 14 mm.
Used copper pan plug gaskets can be reused at least a couple of times by dressing them on a piece of mineral spirits wetted 220-400 paper on a flat surface - like a piece of glass - until the score marks are removed. I've never had one leak after this procedure.
You should use a CJ-4 (diesel) oil readily available at all auto parts stores. The conventional 15W-40 viscosity grade is okay for cold starts down to about 10-15F. If lower cold start temperatures are expected regularly use the "synthetic" 5W-40 CJ-4.
If you want to know why CJ-4, download the following pdf and read the article starting on page three.
http://stlouisncrs.org/news_files/St_Louis_NCRS_Chapter_July_2011.pdf
Vintage Corvette engine or M103 - they all have sliding surface valve trains and need the anti-wear additive level that is in CJ-4. Current S-category oils have less anti-wear additive to protect catalysts from contamination, but they have "roller everything" valve trains and don't need as much anti-wear additive as vintage sliding surface valve train engines.
Duke