The Challenge of Learning Vietnamese

Some of the Western business guys I know have issued a challenge to each other and a 2017 goal ... that is, to learn conversational Vietnamese to a 'proficient' level within 1 year !

It would be a combination of social, business, and everyday Vietnamese.
All are based in HCMC in D1 and their current level of Vietnamese is "non existent".

None of the guys are married to Vietnamese women nor have Vietnamese girl-friends (although at some point they have probably all considered that possibility of a 'local involvement/engagement'). LOL!

All are professional and work full-time, so learning/school time is somewhat limited or varied per week - possibly 6-10 hours per week. Groups sessions are probably unlikely.

We would like to get some opinions of how best to approach this challenge ...
Please offer reasonable ideas, time & cost considerations, best practices, materials, etc.

I was learning Vietnamese via skype. That is great. I studied with good teachers. They helped me a lot. If you want to learn Vietnamese, let try. ivina.edu.vn/ ^_^ Cố lên!