Power Management Unit: How to consider limit to connect electronic component to power rail
If you add lots of bypass capacitors to ensure a smooth clean supply rail, you could use a single big buck-boost DC-DC regulator. Everything on your list will run on 3.3V, as the voltage of a lithium battery can be both above or below 3.3V depending on how charged it is, a buck-boost of at least 2A would be able to give you 3.3V under all reasonable conditions. Otherwise, use a buck or LDO to give you 2.8V for everything except the GSM module (2.8V is a flat battery so the battery voltage should always be higher than that under normal conditions) and use a 2A boost regulator to feed the GSM module, a fully charged li-Ion/LiPo has around 4.1-4.2V across it, if your boost regulator is set to that voltage, the GSM module will always get 4.1V or so.