in order to answer your question, I will need more details, as the operating conditions can affect the type of reccommendation. Temperature, service and duty. If you are wanting to have one fluid that can operate in winter and summer, aswell as offer extended drain potential, then Castrol Dual Range is a good choice.

The use of Bio diesel at lower quantities such as this are now common and in certain US states mandator. Form the work done by OEMs and oil companies, B5 has shown to perform i a similar way to diesel

Supplemental oil additives are never advised to be added to ANY lubricant. Modern lubricants are a careful balance of components to protect from wear, control deposits and heat. Adding a little more anti wear, or more soot handling dispersant usually has undesirable effects on other aspects. e.g. more antiwear can create more piston deposits and poison exhaust catalysts.
We are constantly looking at innovative new components to add to the engine oil, and often include these in some of our fully finished formulas.

Bio derived greases and oils are of a great deal of interest at the moment. Currently the main advantage of all such bio derived products is their effect on the environment, by using less of the valuable and finite sources.
We have had experience of bio greases and found that it is possible to boost the performance upto that of a low tier lithium complex grease, but the inherant poor oxidation stablity of a bio grease limits its performance to that level.

Supplemental oil additives are never advised to be added to ANY lubricant. Modern lubricants are a careful balance of components to protect from wear, control deposits and heat. Adding a little more anti wear, or more soot handling dispersant usually has undesirable effects on other aspects. e.g. more antiwear can create more piston deposits and poison exhaust catalysts.