I would type it. I wouldn't risk the interviewer having to contend with your handwriting (not that I'm saying your handwriting would be bad...). Its just I don't think interviewers spend too much time reading your MH03 before hand, so you want everything to be really accessible to them, when they pick it up and have a look just before your interview starts. I think 350 should be fine, they won't count words or anything. I reckon they put 300 just to stop someone sending in like a 1000 words, because otherwise, they would haha. The most important thing is that your MH03 is readable, get someone else to read over it first. I found that helped, because I tend to understand my own long comma-filled sentences, but apparently no-one else does.