Installing a body kit hard? Yes and no...polyurethane is definitely easier and more forgiving to work with than fiberglass but often times depending on your car the option of polyurethane is slim at best. I made my own side skirts for my previous baby and installed my own bumper...it's not difficult...just remove the bolts holding your front bumper and put the new one on...and just so you know 95% of the time it's never a perfect fit which means a bit of work...before you order it be sure you have the right measurements where it fits around your safety bar...because moving that thing is a b**** and excrusiatingly* time consuming lol...
The fiberglass Type E buddy front bumper I had on my old car I got from extreme dimensions and it was fiberglass, was almost a perfect fit but I had to modify it a bit...I cut it up the middle removed what I didn't need, re-enforced the seem with 1/4" plywood and 1/4" abs in behind, did the body work and then I took it and had it painted. Just make sure you have at least three layers of clear coat on it or it'll chip like crazy. For me because I'm not a professional this took me two weeks to make the skirts and a weekend to get everything fitted and do the body work so it was ready for paint. I painted my skirts myself so if you're looking to paint it yourself make sure you do it indoors cause there's these weird bugs that show up outside lol and use a self etching primer. When attempting anything like this especially on a daily driver, you must have PATIENCE lol..because it's just not pretty if you don't LOL