First off, thanks so much again for purchasing a Nexus 5 to try out Maru!
Which version of Maru are you using? I assume v0.2.2? You can easily check in Settings > About phone
I am surprised you are having issues installing pandoc. I was able to easily install it with the following from a fresh Maru v0.2.2 install:
$ sudo apt-get update
$ sudo apt-get install pandoc
I'm also able to run a quick Markdown formatting test to HTML so things look like they work out of the box:
I don't use ownclient myself so I can't easily test this. But these commands installed the 1.6.4 client just fine.
$ sudo apt-get install owncloud-client
Does the older client not work for you?
Please try the above and let me know how it goes. If you are still having issues please give me the the exact errors you are facing, e.g. paste terminal output etc.
Hope this helps!