Apache Spark: Pre requisite questions
You need to install hadoop-2.7 more to whatever you are installing. 
Java version is fine. 
The mentioned configuration should work with scala 2.12.1.
I am about to install Apache Spark 2.1.0 on Ubuntu 16.04 LTS. My goal is a standalone cluster, using Hadoop, with Scala and Python (2.7 is active)
Whilst downloading I get the choice: Prebuilt for Hadoop 2.7 and later (File is spark-2.1.0-bin-hadoop2.7.tgz)

Does this package actually include HADOOP 2.7 or does it need to be installed separately (first I assume)?
I have Java JRE 8 installed (Needed for other tasks). As the JDK 8 also seems to be a pre requisite as well, I also did a ' sudo apt install default-jdk', which indeed shows as installed:

default-jdk/xenial,now 2:1.8-56ubuntu2 amd64 [installed]
Checking java -version however doesn't show the JDK:
java version "1.8.0_121"
Java(TM) SE Runtime Environment (build 1.8.0_121-b13)
Java HotSpot(TM) 64-Bit Server VM (build 25.121-b13, mixed mode)
Is this sufficient for the installation? Why doesn't it also show the JDK?

I want to use Scala 2.12.1. Does this version work well with the Spark2.1/Hadoop 2.7 combination or is another version more suitable?
Is the Scala SBT package also needed?

Been going back and forth trying to get everything working, but am stuck at this point.
Hope somebody can shed some light :)