Shaktipeethas.org

• It's very much stressed about seeing Moon god. But, if not possible, don't wait until you see him. Offer your prayers to Moon god, Chaturthi tithi and Lord Ganesh at the time of Moon rise. That is much more important.
• Red colored flowers like Hibiscus, Rose and Lotus are encouraged. But, they are not compulsory and you can use others too.
• We should start Puja after Sunset and complete it by Moonrise (May be between 6.00 P.M to 9.00 P.M).
• Actually I don't know any Arti specific to Sankashtahara Ganapathi. One thing I can warn about is, Please don't use the Arti written for Varada Ganapathi, because it will have something like, "I pledged not to see Moon", which is exactly opposite to Sankashtahara Ganapathi, who gave boons to Moon god after being worshiped by him.
• Upavasa is encouraged, of-course, it has many variations like, Nirjalopavasa (fasting with out even water), Jalopavasa(with water), Ksheeropavasa(with milk), Phalopavasa(with fruits, as you told) and many more, depending on one's capacity. After offering prayers to lord Ganesh at the time of Moon rise, we shall end Upavasa by taking Prasad. We can take complete meals and no prohibition is present on that. But, if we are trying to do Jagarana (night-halt), our meals will be simple for the sake of convenience.

What to do if it is not possible to do Vratam because of some problem?
Nama japam is the solution. Say "Gajanana" all the day and offer prayers to Moon god, Chaturthi tithi and Ganesha at the time of Moon rise.

What if we do errs in Puja vidhi?
No body is perfect. It is only lord Shiva who has complete knowledge. Let us prąy lord Shiva, the Adi Guru (who guides us in all our deeds) and lord Vishnu, Yajna phala data (who fulfills us in all our deeds).