How will mesothelioma affect my health going forward?

Not well. Only effective treatment is surgery. Chemo and radiation not effective.
Dificult question. What you feel depends on how good your lung function is overall. As long as it is not compressing on something that hurts, like a nerve under a rib, you should not have a lot of pain but it varies with the person. As the lung in the afected side of the chest gets involved, it wil slowly cut down on your breathing ability so the better you lung function before all this happened the better.