SYN oil does not cure heat. It does however protect the engine from heat better.
As for SYN oils the top high quality syn oil are all great oils and any of them will server you well.
No madder what brand or type oil you decide on it should be oil designed for Vtwin air cooled engines. Auto oils do not have additives the Vtwins need.
EPA required markers of auto oils to remove or cut back some of these additives over the years.
As for same oil or lube in all 3 holes if you would not put gear lube in your engine why would you put engine oil in your transmission. we have many threads on this subject quick search will bring them up.
OIL, LUBE and filers is not a place to go cheap on your bike they are the bikes life blood.
That's my view your ride your decide