I have been wanting to switch to using mainly swiss meringue buttercream as apposed to American buttercream but I am unsure of a few things. 

1. Can you use SMB under fondant?

2. Also when I make it it is very soft sometimes thus making it hard to pipe I'm not sure what goes wrong or if it's too hot in the room. 

3. Is it best to crumb coat first to he handed apply to he Han hick layer of icing or just a thick layer and smooth back? I did a crumb coat n chilled it a bit and when I went to do the final layer it was so difficult and most was coming off and as if it was not sticking to the cake. 

Any tips and suggestions would be awesome. Thanks.  

What is your recipe? There are a few reasons why it may be too soft, one being the ratios in your recipe and two being that the egg whites are not being beaten to a firm enough peak before the butter is added.

Before starting wipe all of your equipment that you will be using prior to adding the butter over with white vinegar. So for me it is the container I crack my egg whites in to, the pot, whisk, spatula, mixing bowl and my whisk beaters.

If you crack each egg in to a container before adding in to the pot or bowl you will heat it in then it is no big deal if you crack a yolk, just add the whole egg to your separated yolks then clean your container before doing the next one - a tiny bit of yolk can ruin your stiff peaks :-( .

I always do a super thin crumb coat, set in fridge and then apply a THICK layer of ganache or SMBC and remove the excess. Never 'lift' the spatula as you apply the SMBC as you will find all your icing lifts too, smear the SMBC on and glide the spatula off. 

Of course you don't want to make way too much buttercream so apply thickly in one spot, use scraper or spatula to roughly remove excess then move on to the next spot, rinse and repeat until all done then concentrate on a smooth finish.  Refrigerating as needed to firm the buttercream for easier smoothing. 

I always use swiss meringue buttercream under fondant.  I love it.  I've actually prefer it to be fairly soft when I frost with it because my cake is generally well chilled.  As said above I too always do a crumb coat, then refrigerate until solid, then do a second coat, then refrigerate again until solid.  As far as why it came off your cake when applying second coat - I'm not sure.  Was your cake cold?  Or frozen?  I've found if my cake is frozen and I'm trying to add a second coat of SMBC it's impossible because of condensation.  One more thought - SMBC must be made in a Kitchen Aid or similar free standing mixer - it will never work using a hand mixer.  The advice above for making the SMBC is good too - yes crack eggs in separate container before putting in bowl.  Here is my recipe - and I think probably everyone's recipe as well (I dbuble it):

http://www.marthastewart.com/353415/swiss-meringue-buttercream

I never do mine in a stand mixer, my hand beaters have a whisk attachment and I use the whisk until I get stiff peaks then switch to the standard blades to add the butter.

I only work with small batches - usually 4 large egg whites, I metric cup of sugar and 360gm butter but  have doubled it and still do it by hand. It is done in 10 minutes easily with regards to mixing time.

I cook my whites/sugar, tip it in to my mixing bowl on an ice mat, let cool for a little bit then beat until stiff peaks form, switch the whisk to blades, put all my chopped butter in which is super soft at room temperature and mix on low until it is incorporated, crank it up and give it a few minutes and I have beautiful, creamy, satiny SMBC.

Thanks I think my cake was too cold when applying final layer since I let them firm up in the freezer. 

And I do use a kitchen aid stand mixer :) 

I will try again and hopefully have better luck.