Hmmmmm....I got the same numbers as you - I would not suggest consistently going below 1200 calories a day. Maybe go for a slower loss - if you plan for 1 1/2 lb a week I came out with 1421 cals a day average. If you bump up the exercise you might lose faster - but you don't really have so much to lose.
As for varying my calories I manage it without trying very hard - I end up going higher on weekends pretty much automatically. (Funny - I don't even have to try?)
I log what I eat in Fitday - it is handy for the reports and being able to look back and see trends. (Also for keeping track of the protein/fat/carb percentages.)
IMO - 4 months to lose 25 lbs is doable - that's only .64 lbs a week. The only thing I might add about that is that sometimes the scale can be annoying when you are building muscle - the scale has a tendency to stop moving...but your measurements are changing. Can I be nosey and ask what happens in 4 months?