I have been asked for a list of the basics and here is what I think you should have to make a good start.

You should have at least 4 or 5 couplers and they can be either the regular 2 part ones or the more jazzy 3 parters...I like the quick change ones but there really isn't a "better" one.

Of course, not shown are icing bags...you will need those and I do suggest you buy disposable because it is sooooo messy if you use ones you have to wash...You can get them in a recycleable material.

These are the tips that you can do most things with...a 3 for line work and writing, 1M for swirls/roses, 2D for Hyrdrangeas etc, a 104 petal tip, a 233 and 352 for grass/hair and leaves. 

The flower nail is important so you can make little flowers and add to cupcakes and cakes as desired.  

The offset spatula and bench scraper are necessary for cakes more than anything and I would advise the purchase of a turntable or lazy Susan.  

And there you have it..Easy peasy, lemon squeezy....