As previously stated, not everybody experiences major side effects from Ofev. Some experience none at all and others have mild or moderate effects. The company will always tell you these are "manageable". Take it as prescribed, with high-protein meals etc.. If the side effects prove to be a serious issue, see about lowering the dose from 150mg/day to 100mg/day. You'll see many people on this site who have done that.
Your doc has clearly determined that it's serious enough to warrant putting you on Ofev so pay attention to what the doc says.
As for pulmonary rehab, this will help you build up your strength and endurance. You have to take it seriously. Exercise every day, at home or wherever you happen to be. If the instructions say "repeat 3 times a day", do it. You won't get any real benefit from doing this half-heartedly.
Also, and this might be hard to take in, but pulmonary rehab will not improve lung function, per se. It enables you to do more with the lung function you have left. The scarring from ILD is permanent and irreversible. That was a very bitter pill for me to swallow because I really thought I would be able to shake off a lot of the worst of it.
You may see a very slight improvement in your PFT numbers if any inflammation goes down but that depends on whether you have inflammation or how much there is.
I wish you well in dealing with it and I hope you have a strong, steady support network.