In reply to Ewol Mullac:
Hi, I went on a similar trip a few years ago. My girlfriend came too and coped with expedition life and the altitude better than I did to be honest! My friend's girlfriend also came and was not pleased about being there at all, but she was a trooper, got used to the whole thing and we all summitted with no drama.
I get very anxious when doing anything new, particularly things which involve logistics and several steps (packing, airports, transfers) to even get started. Once we got walking, the anxiety evaporated, I was very relaxed, enjoyed every minute of it, was far more chatty than my normal introverted self. We had a great group and all the hassle of living out of a tent high on a mountain didn't feel like hassle at all. It was amazing. It was like taking a break from my usual anxious self for 3 weeks!
Personally, whilst it may make sense to hire stuff out there, I didn't as I wanted as little to worry about as possible before I left. Everything got used again on other trips, and can also easily be sold if you don't need it anymore.
Our trip was Mera Peak which I believe is technically slightly easier than Island Peak but it is higher. It was very cold and some people failed to summit because they didn't have warm enough boots or gloves, so don't take a chance on that! The company you're going will give you the advice you need though.
If you're worried about the technical side, crampons, axes, harnesses etc, try a winter skills course in the UK over this winter or just get out winter walking with your gear and practice using it (somewhere safe!).
Hope you have a great time...I'm jealous! And if your girlfriend is reading this, do it too! It'll be an amazing experience and not as hard as you think