yes sure you can, it indicates you're close or you tend to be close to him. yet it's forbidden to call an elder/senior person like this. Otherwise, it's safe to call him surname plus given name.

yes sure you can,but just when you are very knows him very well

如果你们刚认识 --------王朋 ， 王先生 如果你们认识久了， 根据年纪可称呼 ， “老王 小王 朋”等

You can call their family name,because his parents know it，but you‘d better call them full-name，this is habits，in china。

It depends the situation. on a formal occasion, for example, in the office room, say 'Hi 王朋' or 'Hi 王' or family name plus the title '王经理'，'王先生'. And.. if u say '朋', usually u two r in a very close relationship.