Formative evaluation takes place throughout the project. Summative evaluation occurs when there are outputs, outcomes and impacts to assess - usually at the end of the project, or at the end of a major phase of work. See also Timing Evaluation Activity
This will depend on a number of factors, including the resources available. However, bear in mind that external stakeholders are likely to be interested in the impact your project has on its intended audience, so this forms a useful 'boundary' for thinking about evaluation.
Either can be done, but you should always endeavour to ensure an element of independence i.e. even if it is internal it should not be undertaken by the same people who have been undertaking the work being evaluated. If you use external consultants, make sure they have both evaluation experience and detailed understanding of the subject matter.
Yes, it probably does. There are well-established procedures for evaluating research which need to be added to the strategy - most obviously, research is usually subjected to peer review, through published papers and other mechanisms. You will still need to undertake and report on an evaluation of the project's processes, outputs and outcomes though.