How much weight could I realistically lose in 6 weeks?

You shouldnt focus on your weight you need to get the tape measure out! If you go by weight it will be deceiving becasue as you are exercising you will gain muscle (which weighs more than fat) so by weighing yourself you will not get accurate reselts. Its good that you have set yourself a realistic target of 6 weeks rather than thinking you will get results in a week. Measure around your waist, hips, thighs, and arms and record this on a weekly basis. Once you start to lose the inches then you will know all your efforts are paying off! Im not a fan of diets myself as all your body truely needs is a balanced lifestyle. Eat little and often and at least 5 portions of fruit and veg a day -make sure you're getting your protien (white meat and fish) things like nuts seeds and whole grain serials you need too. Its all common sense at the end of the day. Sugar alwasy turns into fat if you dont burn it off so even though a packet of marshmellows for example with prob read "no fat content" the sugar contant will be v harmfull! Expect to drop between 1-2 dress sizes in 6 weeks depending on how many calories you burn. Its all about keeping active!!!! Good luck!!!