No one would be able to provide you a detailed plan here, This is for you to decide yourself based on info available online etc (one such example is Tripadvisor site). If you find it very troubling then you look for tour packages by different local travel companies (many have their online sites with details) and try to look for similar hotels using agoda etc. If you want to travel with controlled budget then there is no shortcut to your own research, else you can always directly book the package of your choice with some company.
Stay length depends on your own budget / choice, I would recommend Langkawi 3 nights, Penang 2-3 nights, Kualumpur 4-5 or even more as per your budget. From KL to LGK you need to fly (best option), LGK to Pen again fly, Pen to KL we used bus service, but you could use train / air also. Mostly of these can be booked online from here so once your plans are final go ahead with bookings.
Money you need to take depends upon your life style and type of vacation you envisage, I think so that if planned nicely and properly budgeted you can have a good vacation for 4 adults within 0.4 to 0.6 Mil (again all depends on your choice of travel, hotels etc)
