how to Install Varnish on Ubuntu 14.04.1 LEMP

Hello, i m running one wordpress site on 512 droplet. i want install varnish for my droplet and i believe i must do some extra things also so that varnish can cache my wordpress site efficiently. just like its described in the following tutorial https://www.digitalocean.com/community/tutorials/how-to-install-wordpress-nginx-php-and-varnish-on-ubuntu-12-04

now my questions are the following

Q1. How can i install varnish for my nginx server which is on ubuntu 14.04.1? i tried to follow the above tutorial which is for 12.04 but that didnt work. says not supported when i try to install varnish. maybe that procedure not supported anymore for 14.04.1 or maybe because that is for varnish v3.

Q2. Currently Opcache code is enabled and its set to following parameter opcache.memory_consumption=128 opcache.max_accelerated_files=4000 opcache.revalidate_freq=60

should i change them to default or keep them as it is? or i simply dont need Opcache anymore?

Q3. i need to add one sub-domain that will bypass varnish cache and hit directly to my nginx server which is on default port 80.