1: if its bodybuilding your interested in, dont worry bout losing the excess tyres mate. do that later in the year leading up to summer when you will get a real chance to show off the goods so to speak... you will lose a bit of bodyfat over the course of your trainin anyway
2: i would highly reccommend a gym... the atmosphere i found really helps keep me motivated, and you can make the most of the vast amount of available equipment, although for the first few months, you really shouldnt need to use a lot in the way of machines- stick to compound movements that maximize strength and size.
you can certainly do ok at home, but i still prefer a gym. plus, you can get a PT to keep an eye on you for the first few workouts to ensure you are doin the movements safely and with form
3: to start, try 3 days a week for the first month or so, then 4 days a week thereon in (time permitting). i train 5 days a week, but i got time coming out the wazoo!! ;D
good luck with it all.
as you may have noticed, correct eating habits and diets are constantly comin up on this forum, so dont neglect diet in particular