I actually have those too but I'm interested in starting out small.
You have the entire Menaion in English? If you come across a used copy of the HTM one, please let me know!
Between the Midnight Office, the Hours and the Compline which is the easiest for a humble newbie to take on?
None of them are particularly difficult. The Hours are the shortest, then Compline, then the Midnight Office. All the material you need is contained in your Horologion. The instructions are easy to follow, and the variable parts (basically just the daily dismissal hymns, and the Hypakoe for Sundays) are easy to locate.
Typically, the Midnight office is read when waking up, the Compline before going to sleep. So it would be good to familiarise yourself with these two first.
That being said, I find the Hours to be a great help during the day - between classes, on the train/bus, etc. The structure is the same for all 4, so you'll become comfortable with everything fairly quickly.
It's the HTM, a rather large red tome. So it's Greek...
I have both, and the HTM publication is far superior imho.