1. While the law on the legal profession has provisions on pupillage, there are no fine detail on how it must be done. It is one's choice whether to do pupillage in a specializing law firm or an all-practice law firm - of course, one must be good enough to be recruited first by the law firm. There are not a whole of of firms in Ghana specializing. It even appears to me that - in the more developed countries - there is a move-back from specialization to all-practice 'boutique' firms again. You have to decide where you want to do your pupillage for yourself - bearing in mind what you want to practice in. Personally, I would more likely advise an all-practice.
2. There is no reason why you cannot specialize in "crime, contracts, employment, corporate law and wills & probate." But you may make the practice more 'rounded' by putting employment under corporate - because that is how it works usually - and doing family law - instead of just W & P. You need to think about whether you want to do criminal law together with the rest - which are all civil law. There are many factors of workload. One may be how many areas of practice you take up. I suspect however that the bigger factor is simply the quality of your clientele, complexity of matters you are dealing with and numbers of matters too.
3. Pupillage runs for 6 months - sometime after you are called to the bar in Ghana. It does not have to be immediate but - without it - there is a solicitor's certificate you need - but cannot obtain - to practise. You can only lawfully do pupillage under a lawyer who has practised the law for at least 7 years. Most people like to do their pupillage immediately after the call to the bar.
4. It is difficult to call any area of the law developing as such in this emerging economy. Let me rather tell you about industries which are promising - and they will need legal advice! Telecommunications is hot - I think. The financial services are hot too. There are many Small and Medium-Scase Enterprises in need of day-to-day legal guidance in all manner of matters. I have to say Oil-and-Gas too, although I admit I have a personal skepticism about whether it will really become 'hot'. I think 4 out of every 5 post-graduate degrees obtained by Ghanaian lawyers now will be in Oil-and-Gas. M&As are still not big in Ghana. Competition law is nascent at best. On another level - dispute resolution - Arbitration is fast gaining on Litigation as the preferred means of resolving disputes, especially by medium and big corporations.