Job offer : good enough to save and live decently in RAK ?

RAK is cheaper than Dubai and AD for sure in terms of living costs.  It is pretty small.  While I don't have exact details on costs for a 2 bed villa; you might want to go to Dubizzle and browse the listings to get a general idea.

In terms of salary and qualifications; look, this varies quite a lot in this part of the world and is dependent on company, location, nationality etc.  For example, CFOs could be paid 100K AED monthly for a big listed or multinational company vs. say, 30-40K AED in a local company - despite similar qualifications and years of experience (same title but very different responsibilities and compensation).   So it is very difficult to generalize.   To get an idea of the range, go to the middle east websites of recruitment agencies like Robert Half, Michael Page and Hays and browse their free salary surveys to get some idea.

On the face of it, the total cash seems adequate to support family of 2 and still save.  If you end up having kids, that is a much higher cost and in that situation, you would need to negotiate schooling with the employer.

Lastly, the salary breakup is VERY strange.  8K basic and 27K allowances?  it doesn't make any difference in terms of the cash that you get but will make a huge difference in terms of end of service benefits or upon termination as basic salary is what is used to calculate these (and basic salary is what is registered with MOL in their official records).    Employers sometimes do sneaky stuff like that to reduce their EOS costs.