Looking to get in shape any tips.

Hi All new to the cycling world, well apart from when i was lad. But being 33 and way out of shape. Time has come to beat the gut. lol Got my self a nice mountain bike 24 gears bla bla, The guys in the shop set the saddle and the like, as I have no clue. Just wondering what is the right way to go about it. how much is to much, same for not enough. At the moment im cycling too and from work. Works out as around 30k a day. Been biulding it up the last few weeks. 1 day cycle in miss the nexted and so on. Till now I can just about do 5 days.Have to say the legs look great lol. But when does the effect take place in the rest of the body lol. Not sure really how its works. Im heading over to New York at the end of the month so I will be getting a HRM there as there a rid here in Ireland. Any advice on whats best to eat wheat to give a miss and the like. Is 150k aweek enough. Feel alot better But find the cycle home is not as hard as the cycle in. Going home its up hill. This is all over the place so if u can make sence of it, Like to here from u. The Fat Man Ireland lol