You really need to have a separate room in my opinion. As a remote worker you save a lot of money not travelling and spending money on lunches, and/or can live where space and housing is much cheaper, so this is possible. I built a home office: https://rwmj.wordpress.com/2013/07/10/garden-office-most-mos...
No I hired a couple of people to assemble it (for about $1200). It certainly would have been possible to build it all on my own - it's just a big, complicated shed kit after all - but it probably would have taken me a month so it made far more sense to hire them. I did give it three coats of paint and stain inside and out though!