Al-jawab billahi at-taufeeq (the answer with Allah’s guidance)
1) If you do not owe an expiation (Kaffarah) then you are obliged to make up any fasts you missed. If you have a lot of missed fasts, then you need to make up a schedule. You can easily discharge this obligation by fasting on the Sunnah days, such as every Monday and Thursday, or the Ayyamul Beedh (White Days), which are the 13th, 14th, and 15th of every lunar month, or the fast of Dawud (Alaiyhis Salam).
2) To masturbate will break one’s fast. To make up for it, all you will have to do is make Qadha of that day. Kaffara (expiation) is not necessary. (Imdaadul Fattah Pg.691/ Hashiyatut Tahtawi Pg. 664)
One should also make Taubah too.
Allaah Ta’ala says : “Say: ‘O My slaves who have transgressed against themselves (by committing evil deeds and sins! Despair not of the mercy of Allaah; verily, Allaah forgives all sins. Truly, He is Oft-Forgiving, Most Merciful’. [39:53].
3) Eating and drinking intentionally will make both Qadha and Kaffarah necessary. (Nurul Idhah Pg.142)
Also, to eat and drink forgetting that you are fasting and thereafter thinking that the fast is broken, to eat and drink again. Qadha will be Wajib only. (Nurul Idhah Pg.145)
And Only Allah Ta’ala Knows Best.
Moulana Qamruz Zaman