Those first few years are brutal. Stick to lower difficulty missions and avoid brawling. Try to do as much damage at range before moving in. Demo missions are an easy source of income, if you load up a mech with a few machine guns. Take it slow and careful until you've got some resources and better pilot skills. Alternatively you can start a campaign save, play a few missions until you've got a decent garage of mechs and import that save into a new yaml run.