Safari is not what takes up the most disk space so why not leave it? Besides what if curiosity gets the better of you and you really want to test-drive it one day and give it a real try?
I would have to agree. In the grand scheme of it, internet browsers are not going to take up that much of your HD space. There really is no reason to remove them. Besides, it is always good advice to keep a few different browsers on hand as some will have difficulties displaying some sites and others would do just fine with them
If you are that concerned about saving drive space, then I would look into other things you have eating up your HD.
Yes, you can safely ditch the MS Office trial. I would also ditch other trial software and sharewares, as they are more likely to consume your drive.
If you have a large number of movies, images, and songs, then an external drive would be the better solution, opposed to deleting applications.