Understood that especially in front-end work, dual screens are pretty much necessary for testing & debugging and just being able to work efficiently.
FWIW, a 24" monitor in original box will fit in a checked bag-- takes up half of the medium-large hardshell luggage I have-- and yes I've traveled with an extra screen.
I think the question really is, does it do anything for file size? If there were a radical difference in total size, the quality degradation might be an interesting compromise.
There are a lot of resources out there for contracts-- which you should definitely be using-- andFreelancer's Union also has some good tax and contract guides-- https://www.freelancersunion.org/resources/ (They're free to join.)
The main thing to remember is that if the total value is over $600 and you're reporting the income, the company will likely ask for a W-9 from you and issue a 1099 at the end of the year. Then, you will be charged the 15% self-employment tax on top of federal and state taxes. A lot of beginning freelancers don't figure this into their rates, and they end up with a much bigger tax bill at the end of the year than anticipated.
I would recommend charging hourly, $50-75/hr is likely reasonable in your area, but providing the business an estimate of the range of hours-- say 10-15, or 20-25, etc so at least they know ballpark in the beginning what to expect. If you check in with them midway and say "hey this is ending up to be a lot more complicated, just so you know it will take more hours" then they'll appreciate it and be more likely to pay you quicker with no quibbles or "surprises."
It really depends on your skillset... if you code or do creative work, building a theme, shooting stock photography, or creating music with low licensing fees are all good things.