The simplest way to run your analysis (without trying to define your actual inputs) is to do some basic raster algebra.
Have a go with the raster calculator: https://docs.qgis.org/2.8/en/docs/user_manual/working_with_raster/raster_calculator.html
You can build up some other vector layers too, such as 'distance to waterbody' as a distance raster.
To combine them, look into Multi-Criteria Decision Analysis (MCDA) https://en.wikipedia.org/wiki/Multiple-criteria_decision_analysis
The basic idea is that, say you have three rasters R1, R2 and R3 and for each cell (and the rasters should have the same extent and cell size) you're calculating an index by saying:
IND = R1 + R2 + R3
You can also weight this, by defining a weight for each raster, and combining that, so:
IND = (W1 * R1) + (W2 * R2) + (W3 * R3)
Additionally, it is normal to scale values for each raster so that they are between 1 and 0, you can do this by normalising each raster. If you're normalising then ensure your weights sum to 1, differences give you prioritisation of each factor.
Finally, you can have 'hard' factors, so, you might exclude the ocean from your study. Get a raster of your ocean, and classify that as 0 = ocean and 1 = not ocean. If you multiply your IND by that OCEAN layer, you'll only have values in the cells that aren't ocean.