Looking for studies on introducing registrations

Our website allows users to draw plans for submitting to local authorities for planning permission.

Currently we don't force people to register, although they can choose to do so to save their payment details.

As such we have a few 'issues,' one is we have no relationship between an awful lot of users, the second is the value added services such as the usual account related ancillary items like saving your plans, checking your plan creation for accuracy etc.

We are currently floating a few ideas to get people to register. The first idea is 'hard registration,' the site would operate as now, you would enter your postcode, find your address and the next button would ask you to log-in if you weren't or register if you are not.

The second is a softer version, where users who go through and create a plan are encouraged to register at the end of the plan creation.

A further consideration is the method of registration, do we go for traditional email and password or allow users to use oAuth providers like Facebook, LinkedIn etc. bearing in mind, many of our users are professionals like architects and planners.

I'm looking for data/studies to show the effect of forced registrations or soft registrations

So we can take a view on the best UX practise if we choose to implement this and the method of implementation.