Glad to hear that you are keen to know about festivals of other religions. It is good to learn with an open mind about the traditional legends, holy books, and festivals of any religion. Answering you specifically
A. What kind of sweets will be prepared for this festival?
Bal Ganesh is always portrayed and known for his love for sweets and hence sweets form an important part of any Ganesh Chaturthi function big or small.
The popular sweets are
1.Modak. The modak can be either steamed one or the fried one. It has a central sweet filing and an outer wrap of thin rice flour based sheets.
2.Puran Poli- popular in Maharastra, it looks a thin chapathi that has a sweet jaggery+lentil mix inside.
3.Ladu(can be the classic motichoor-small grains like boondi or a coconut ladu).
4.Shirkand- sweetned set thick curd dish
5.In South India, we use Payasam and Sweet rava pongal.
The other sweets into Karanji ( like a stuffed pastry of dry fruits and sweetened coconut flakes), patholi(steamed stuffed sweet rice rolls). Each region in India and the commercial sweetshops make many variants of the above that are unqiue to the various parts of India. You can visit any of your friends or just go shopping during Ganesha festival in your city and see the display in the sweet shops.
B.And when will people be celebrating this festival?
The week to ten day long festival start on the auspicious 4th da of the Hindu calender, this comes between the second part of August or the first part of September. This year it comes on 13th Septmeber 2018, last year it was on 25th August 2017. The celebrations range for a single day to 10 days. Many local areas in the villages, towns, and cities have a common pandal with a large idol of Lord Ganesh and daily poojas are offered.
C.What is good about it, and what is bad about the festival?
Like any festival of any religion, it brings in joy and a spirit of oneness in families, localities and community. It is a festival that ushers in Fortune, wisdom and success.
There is nothing bad about it, some environmentalists would comment about the idols immersed in the smaller lakes, leading to pollution. This is also getting better with many people going for simple clay idols that do not pollute too much.
C.What are the customs of this festival and what are the Rituals?
The custom include bright decorations, idols of Lord Ganesh in various sizes, regular poojas, various types of sweets. Women and groups of small children try and visit as many houses where Ganesh festival is celebrated to invoke His blessings.
In many states, one day is celebrated as Gowri pooja, to pray for Goddess Gowri or Parvathi, the mother of Lord Ganesh, usually a smaller idol of the devi is kept next to the Ganesh idol.
On the last day, there is a procession by the local youths and people, then the Lord is immersed in a lake or a pond with a grand function that marks the end of the festivities.