Adwords is usually, together with branded SEO, the top performing channel. But it will only be the best for each advertiser depending on many factors: competitors & competitive advantage (if your competitors biddings are very high, or if your product will not have a good conversion rate), type of market (if your product is related to keywords that nobody search or if it has a high search volume), web structrure (if you have different pages related to different potential searches which can bring traffic to your website, as it will improve quality score, reduce cpcs, and improve conversion rate), etc etc. Regarding affiliate program, it depends on industry and region/country, and the type of affiliates/actions you will ned

You should use all the tracking systems in Bing, Facebok, etc, so you know how much they are contributing to business. On the other side, you can use Attribution (different models) and Assisted Conversions reporting on Analytics, so you can find out which channels are closing the sales and which ones are opening them.

Honestly, i would not pay anything like an hourly/monthly fee, or at least not 100% on this. It should always be linked to results (% of margin, growth, etc), so that the manager is focused on improving the performance and earns direct benefit from it. I'm currently working as an Adwords consultant for a company and our agreement is x% of the net margin (margin - adwords investment)