score:4
1. is adding a pay slip for April 2015 to new bank statement and corrected income on visa application enough?
It should be fine as long as all of the bank deposits correspond to a salary slip and there are no irregularities in the movement of funds to and from the account.
2. How do we handle his self-employed work for which we have no evidence as he trades mainly in cash? should we just delete that from the application?
No, it should be included because it impacts his apparent life-style and explains why he has been able to save so much. Otherwise they will not find his savings versus salary believable and they will not be happy about it. The 'best practices' for that situation is to include a few years of recent tax returns which help show the funds have been legally obtained and accounted for. You can optionally add a statement that explains how cash payments are common for that line of work, and show how it ties in to his tax returns.
4. is providing a receipt of foreign exchange transaction plus an explanation of the 7000 GHS withdrawal enough?
Yes, this should be fine. They will be looking for an explanation supported by some evidence.
Adding...
Trying to fund a visit solely from one's savings account is a difficult proposition because it can look like your husband has saved up for a permanent move there. And if the amount for the visit is disproportionate to the total amount of savings, they are entitled to make that conclusion. What this amalgamates to is that you are avoiding an awkward situation by replacing it with a situation that is just as bad, or worse. Try to spend a proportionate amount on the visit which does not deplete your husband's savings.
Adding...
In commentary, you added that your husband does not have tax returns. If he is working for cash-in-hand the assistants who verify all the information may conclude that he is tax delinquent. This is a situation to avoid because they are entitled to assurances that people will respect the laws when they are in the UK. The 'best practices' for this is to file retrospective tax returns so that all periods are covered. Doing this may delay your plans, but it will help prevent future refusals.
A generic note on Ghana: Ghanaian applications go through the British High Commission in Accra. This consulate is legendary for its staggeringly high refusal rate and sometimes even lawyers are reluctant to take on casework for Accra. A lot of refusals come from people who have been earning in the black market and are unable to properly explain their financial status. This is complicated by the relatively poor performance of Ghanaians overall. Applications submitted to the issuing post in Accra need to be prepared with precision and the most exacting diligence. Legal counsel can almost always be helpful.