1. Gold crowns are stronger, healthier and less tooth structure needs to be removed. Full gold crowns are generally recommended for molar teeth. If you are concerned that the gold will show, ask the dentist to have a porcelain front put on the cheek surface but keep the biting surface gold.
2. Yes, composite fillings will stain in time. These veneers are not a priority for you right now. I'd suggest have the composites placed on these teeth, add milk to your tea, cream to your coffee and switch to white wine
Composite fillings have come a long way in the past years and they are not as porous as they once were.
Use a toothpaste like Crest's Vivid White to help control the staining.
3. Can't always tell how much decay is there with an X-ray. What he is seeing is that it is close to the nerve. If, when he's cleaning the decay out and the nerve gets exposed, then a root canal will be needed. Sometimes they will place a sedative dressing to see if the tooth is going to cause problems. If it doesn't, then a filling is placed without a root canal.
4. Is the tooth loose? If not, keep the pocket clean (5mm IS reversible). If you were my family member I'd leave the tooth where it is. An implant can be placed at any time. I'd go for the root canal, it could buy you a number of years.
5. If you have open areas of decay it makes it difficult to do a thorough cleaning. If you need quadrant scaling why don't you schedule the scaling the same day he does work in a particular quadrant.
My feeling in regards to this is that having healthy gums can make the restorations easier to do as the DDS doesn't have to deal with bleeding caused by unhealthy gums.
PS: He's been poking around with a periodontal probe and explorer. Take some Tylenol and you should be more comfortable.
I hope this helped.