exchange 2013 redundancy with edge transparent

Hello

we have one exchange 2010 and I am trying to upgrade to 2013 with failover.

we have about 300 users.

I have done research and this is what I think right way to do but to confirm.

I want to install CAS and mailbox on the same box and edge transparent in DMZ for OWA access.

everything will be dual. 

1. install win 2012 R2 with exchange 2013 with CAS and mailbox roles on two boxes

2. install edge transparent role on two separate boxes which will be in DMZ

my questions are, 

is there any other option than using hardware load balancer for CAS/mailbox failover?

is it recommended to use DAG or I have to use DAG, even if I use hardware load balancer?

for edge transparent failover, what is recommended direction i should go?

Thanks