Operational Turnaround specialist | Ex CEO and Board Director of European listed companies (IT & Metals) | Management Consultant | Delivered over $160M in sustainable efficiency benefits to blue-chip clients | Developed Operating Models and wrote Operating Manuals for the 2 biggest building material manufacturers | Business modelling and operating performance advisor to SMEs | Founder of www.top10esports.com | Speaks 4 languages
Every case is different but I would expect something as follows. You would probably start with between 2 and 4 people and probably end up at around 5-7 people. They key here will be the people generating the income for the business; both sales and delivery. At $1M you probably would not have an office manager or many ancillary functions as they cost money. You would potentially outsource your accounting. If your sales staff/person is very good you would start with selling one or two project. As these are being delivered next ones would be sold and so on until you cannot deliver more and you have to hire another consultant. At this stage you would probably take in contractors until you are certain of the project pipeline. This will differ for FT projects and PT projects. It will also depend on the daily rate you are charging. If the daily rate is $1k then you are looking to sell 1000 man days to get your $1M => 4 guys working 250 days per year. Add 1 sales guys and 1 or 2 junior staff plus office costs etc. The time of this can take is as little as 6 months or it can be 2 years - all depends on your sales.
As Nikki said, it does depend on the product. The answer also depends on your marketing strategy. Market place as such will not do your marketing you. For end users there is ebay for for pan-European, Tradera for sweden and many other local ones.
It all boils down to how good you are at selling your services and finding clients. As others have said, there is a need for this type of service, question is whether you are able to convert that need into clients.
I would start by doing some market research on how to find potentials and how to convert them into real clients. Only after you have an idea how to do this and, the effort required, can you decide if this is really for you. There will be questions regarding your credentials and why you are so good at this. Also, do not forget the value-add for your clients, how will you ensure they are getting value for money (and that they are aware of it).
Plugin is easier to install and just go for it. Running a sub directory will require more wordpress and name server setup knowledge including potential secondary wp installation.