If you want to develop a MMO, you need to commit to it. Even a text-based game can require a considerable amount of code, especially if you really want to grab the gamers attention and create an addicting and memorable gaming experience.
Roughly, you can have anywhere between 30-100+ files for a descent scale MMO (depends on what type of features are available in your game), with each file containing anywhere between 300-1000+ lines of code. So again, you need to committ to it, you need to put a lot of time and effort towards the project if you want it to be successful.
A hint I learned while searching the inter web: Don't try to make the "bestest-ever" in your first project, you'll never finish!
In terms of programming languages, PHP is probably the best choice for a text-based MMO. It has a small learning curve and there are all sorts of resources online. Since I have never coded in PHP before, I suggest using a free bulletin board like PhpBB and start installing custom mods. This will give you a feel of how to do PHP coding. Once you are a bit more confident, you can install a forum game mod like ADR (Advanced Dungeons & Rabbits) which will introduce you to the world of MMO text-based gaming.