Having gone through it, I got to eighteen stations but some of the articles leave a gap for further new stations in addition to those advised in the document.
If I remember correctly the plan was only a list of proposals that could or not happen, each of the schemes was to fully evaluated before any firm proposal were announced. With some of the proposals in the plan being extensions of the existing Merseyrail network involving existing Northern operated routes, it would be reasonable to assume that any plans would need to be approved before the new Northern franchise is announced next year at the absolute latest. Furthermore, any extensions to the network would likely only involve some rebranding of existing structures and bringing them under the control of Merseytravel rather than new constructions in the majority of cases. The other issue to consider is that a decision on the replacement of the 507.508's is also pending as they are due to go off lease in in 2018/2019 so any decision especially on purpose built new builds will need to be taken fairly quickly to ensure service availability in time. A final consideration is the reintroduction of passenger services to current freight only lines, which in reality is probably only the Bootle Branch and the North Mersey Line which in total would account for about six of the thirty stations alluded too in the plan.
With a new station at Maghull North and St James mentioned, and the Halton Curve due for completion in 2017/2018 which could allow a new station on the line, plus a reopened Ditton, with Mossley Hill, West Allerton, Frodsham and Helsby also coming under the Merseyrail banner, whilst a new station at Sefton Park and/or Wavertree have also been mentioned making a total of seven or eight stations. I haven't included Edge Hill because of it's capability to handle other services whilst Runcorn is also serviced by Virgin and LM.
Extending the Kirkby line would likely involve new stations at Kirkby (Headbolt Lane), Rainford, Upholland, Orrell, Pemberton plus potentially Skelmersdale with Wigan Wallgate being operated with TFGM which might give five more.
Extending Ormskirk to Preston would involve Merseyrail stations at Burscough, Rufford and Croston adding another three to this list.
On the Wirral the only new opportunities would be on the Bidston to Wrexham line which would bring in Upton, a new station just east of Woodchurch Road, Heswall and Neston adding four more to the list. I'm assuming the Welsh Stations on line remain under Welsh control.
I make that nineteen or twenty stations unless they were also counting existing stations in the Merseyside boundary on the Chat Moss and Wigan routes which would take it nearer thirty stations, but other suggestions are welcome.