European Union recently has had grand 10-year strategies - Lisbon strategy for 2000-2010 and Europe 2020 for 2010-2020. Now the debates have started about next multiannual budget for 2021-2027 but I have not heard about debates about strategy program for 2020-2030. So - is it customary in European Union to debate budget before the strategy plan? How previous strategies - Lisbon strategy and Europe 2020 guided the previous budgets (if at all) and does the EU have custom (or maybe even rules) to make strategy first?
There are already targets defined for 2030 such as the Energy Union and the Climate and Energy Framework (in fact you'll even find some for later such as the 2050 low-carbon economy), among others. Also you have the more immediate European Commission Priorities.
The budget is not independent of the strategy, priorities (or Reference Frameworks), and it's slightly more complex that what you seem to be describing. The actual budget of the European Union happens every year. It's proposed by the European Commission, and reviewed by the European Parliament and Council.
The yearly budget must be within the ceilings decided in the Multiannual Financial Framework (which is what the draft proposal of 2-May-2018 is; and it's not finished). So the "Budget" Proposal of 2021-2027 is actually something along the lines of "percentage of EU money you can spend for each of the categories". The current categories are the following:
Sustainable growth 1a. Competitiveness for growth and employment
– research and innovation, education and training, trans-European networks, social policy, economic integration and accompanying policies. 1b. Cohesion for growth and employment
– convergence of the least developed EU countries and regions, EU strategy for sustainable development outside the least prosperous regions, inter-regional cooperation.
Preservation and management of natural resources Includes the common agricultural policy, common fisheries policy, rural development and environmental measures.
Citizenship, freedom, security and justice 3a. Freedom, security and justice
– justice and home affairs, border protection, immigration and asylum policy.
– public health, consumer protection, culture, youth, information and dialogue with citizens.
EU as global player Covers all external action ("foreign policy") by the EU. Does not include the European Development Fund (the European Council and Parliament rejected a Commission proposal to include it in the EU budget).
Administration Covers the administrative expenditure of all the European institutions, pensions and EU-run schools for staff members' children ("European Schools").
Compensations Temporary heading which includes compensatory payments relating to the latest expansion of the EU.
Also the ceilings are reviewed every year based on the adjustment of the Financial Framework:
The ceiling for payment appropriations are also expressed as a percentage of the EU's estimated GNI (based on expected GNI development).
This percentage is updated every year on the basis of the latest available GNI forecasts in the framework of the technical adjustment of the financial framework for the following years. This makes it possible to check whether the EU's total estimated expenses (payments) are within the ceiling set by own resources decision also expressed as a percentage of GNI (1,23%).
So the current Commission, Parliament, Council, etc. - are not making the decision for all future versions of the same institutions. They are making sure that it exist a base plan (which will likely be reviewed, modified, amended many times).
This will probably lead to the question of the why? Why is this process so complex and filled with grand plans covered by smaller plans (and those covered by even smaller)?
RE: Because unlike a sovereign nation, the EU cannot incur in debt. So when something happens (like a refugee crisis, or eurodebt crisis) there is no extra money coming from somewhere in a urgency. This is the reason why the current proposal states the following:
2. A modern, simple and flexible budget
Flexible: Recent challenges –especially the migration and refugee crisis in 2015 – have clearly shown the limits of flexibility in the current EU budget to react quickly and effectively enough. The Commission's proposal therefore includes increased flexibility within and between programmes, strengthening crisis management instruments and creating a new "Union Reserve" to tackle unforeseen events and to respond to emergencies in areas such as security and migration.
So the current idea is to give even more flexibility for future budgets.