i am assuming when you say safe you're meaning security?? there are some horror stories out there, that's for sure.. my advice for someone just starting would be stay away from the cracked apps and you will be fine. also, when jailbroken, you will have the ability to change the root and mobile passwords on the device to help prevent certain situations, but that can be later on when you get more comfortable with everything
as far as being "buggy".. it's all relative as to what you put on your device. there are 100's of apps and tweaks out there that you can use, for free even, but are not it written (coded) very well and in turn make your device "buggy". keep in mind it's typically not the jailbreak that causes imperfections, it's the crap we out on our device afterwards
as far as going back to a stock or vanilla device--easy. just plug your device into iTunes select the Restore option and towards the end, when given the option, set up as new phone. you will lose all traces of the jailbreak but it comes with a price too. all of your other data as well. of course you can save photos/music/apps like normal but you will have to re-enter all of your vital information like when you first set up the device. this can be time consuming but a small price to pay in my opinion
i would like to suggest one thing before jumping into this. research and study for a while--maybe even a couple days or so. i did this for about a week before i did it, just to get familiar with the processes and lingo. take your time. jailbreaking opens up an entire new world but can become very daunting if you do not do your homework
lastly, there is a lot of info here in this forum that when using the search function WILL be very beneficial for you or anyone else if needed. in fact it probably wouldn't hurt just to continue using this thread for all of your questions or concerns until you get more comfortable. there are a lot of helpful people here but to be honest, just like in life, if they see you are willing to take the time to learn for yourself they have no problem helping you
good luck