Ben if you have ridden the 125 for three years winter and summer then you will be aware of most of the pitfalls.
Larger bikes- are a great benefit however with power at the back wheel come responsibility so don't gun it out of every corner as you will soon come unstuck. Minor slips and slides are normal and you will get use to the feed- back from the rear wheel, it's all about control and confidence.
Looking after the bike. - Keep the handle bar controls free using WD40/light grease/water repellent. Pay attention to all the usual problem areas tyres, brakes, lights etc. at least weekly. Frame paint work etc can be coated in a suitable spray. Don't clean the bike after each ride it will drive you insane in a week but do clean and inspect it during daylight hours at the weekends. Forget immaculate!
Riding daily your kit will take a hammering so have at least two of everything and use various combinations to match the weather. To stay comfortable you will need to become good at assessing the weather and act accordingly. Best rule is to 'dress like an onion' in other words many layers of light clothing and not one thick item. Keep the cost down by being imaginative ie using poly bags (inside your boots) and plastic gloves(from the garage- inside your winter gloves).
Ensure you have breakdown cover and carry an emergency kit small tourch,phone, money,good quality tools,bungees,bulbs and puncture repair kit.
And one last thing I am a fat basta*d so I find eating a breakfast before setting out for work helps.
Ask Gizza and the more experianced riders they should be able to help ............... if they can stop taking the piss for 5 minutes!
Hope this helps.