if you update your current 3.0 database to 3.1 it will stop being a 3.0 board. there is no testing or going back.
if you want to test you need to export your database to your computer or otherwise make a copy of it.
install a new 3.1.4 board either on your computer or on your server in a different folder and then import your 3.0 database to it and then run the install/database_update.php file and it will upgrade the database to 3.1.4
then you can test or whatever you want to do to it and it will not affect your live board in any way.
as far as styles go, there is nothing to sort out. none of the 3.0 styles will work with 3.1
prosilver comes with 3.1 and there are now several styles available for it and many more in development.
I would suggest you check out the 3.1 styles and find one you like.
then simply update your board and install whatever style you want and you will be done.
also, none of the 3.0 MODs will work with 3.1, it uses extensions and there are many available so you need to check them out as well as the styles.
I'm baaaaaccckkkk. still doing work on donation basis. PM your needs.
Premium phpBB 3.2 Styles
If a tree falls in the forest and nobody is there, does it make a sound?