The four cups of wine
What type of wine
- It's preferable to use red wine.  If there's white wine that's better than the red wine, Ashenazim say that one should have the white wine, while Sephardic practice is to have red wine anyway.  There is a dispute if it is permissible to mix red wine into white wine to color it. 
- If one hates wine or if it gives him a headache (but not if it's going to make him sick in bed), nonetheless, he should try to have the wine to fulfill the mitzvah of the four cups of wine. 
- Many authorities say that one may not use grape juice for the Seder, however, if one hates wine or will become ill, then there's is what to rely on to have grape juice.  Others, however, permit having grape juice and adds that lechatchila women and children can use grape juice. 
- Rav Heinemann holds that one may dilute wine with grape juice or water down to the point where the wine will be 4% alcohol.
Making Birchat HaGafen
- The Ashkenazi minhag is to make HaGafen on each cup of wine and a Bracha Achrona only on the last one. 
- The Sephardi minhag is to make HaGefen on the first and third cup of wine and a Bracha Achrona only on the last one. 
- There’s no Bracha Achrona on the first cup even if one knows that one will take longer than Shiur Ikul in explaining the Haggadah. 
Drinking at other times in the seder
- One may drink wine in between the first, second, and third cups of wine but not between the third and fourth cups. 
- Even though one is permitted to drink between the first and second cup, one should be strict not to wine too much wine so as not to get drunk (and not be able to say the whole Haggadah). 
- According to Ashkenazim, in order to be permitted to drink between the first and second cup one must have had in mind to drink anything that comes later or that the wine was in front of them when he made the bracha (as long one didn’t have in mind not to cover that drink) because in this case no new bracha is needed on the wine between the first and second cup. 
- It’s totally permissible to drinks other than wine or intoxicating beverages between the first and second cup. 
- It’s permissible to drink between the second and third cup. 
- After drinking the four cups, it is prohibited to drink any other beverages, besides water.
If four cups are drunk all at once
- If all four cups are drunk at once and not dispersed throughout the Seder in their proper place one doesn't fulfill his obligation. 
Amount to Drink
- See the Required Amount of Matzah and Wine for the Seder page.
Obligation to Lean
- One must lean while drinking the four cups of wine. If for any of the cups one did not, according to Sephardim, one should drink the cup again.  According to Ashkenazim, only for the second cup should one drink the cup again. 
- Chazon Ovadia (pesach page 1). However, Rav Shlomo Kluger in Sh"t Kinat Sofrim 95 holds that the obligation of the four cups of wine is from the Torah.
- Shulchan Aruch 472:11. Mishna Brurah (472:38) explains that the idea of having red wine either reflects the verse “Do not look at wine when it is red” (Mishlei 23:31) or serves as a symbol to remember Pharaoh slaughtering the babies of Bnei Yisrael and bathing in their blood.
- Rama 472:11 writes that if the white wine is better one can have that instead of the red wine. Kitzur Shulchan Aruch 118:1 concurs. Kitzur Shulchan Aruch 118:1 adds that in countries where there is a fear of a blood libel, the minhag is not to use red wine. However, Chazon Ovadyah (Pesach vol 2 pg 11) writes that the Sephardic custom is to use red wine anyway. Rav Mordechai Eliyahu (cited by Mikrei Kodesh (4:15, n. 52) says that the "tirosh" grape juice in Israel that has a yellowish color is considered red wine in this regard.
- Mishna Brurah (320:56) cites a dispute whether it is permissible to mix red wine into white wine to color it or one should avoid this.
- Shulchan Aruch 472:10 says that even if one hates wine or it is harmful to his health one should push himself to have the wine to fulfill the mitzvah. Mishna Brurah 472:35 explains that one only has to have it if it gives one a headache but not if makes one sick in bed.
- Mikrei Kodesh 2:35 (pg 130), Sh"t Chazon Ovadyah (in the note on pg 99-100), Halachos of Pesach (chapter 20, Sec B 5, pg 222) quoting Rav Moshe Feinstein rule that one doesn't fulfill חירות- having wine as a free man by having grape juice. However, Halachos of Pesach concludes that if one is unable to have wine one should have grape juice. Teshuvot Vihanhagot 2:243 writes that the Chazon Ish, Brisker Rav, and other Gedolim used grape juice at the end of their lives when they were unable to drink wine. Rav Shlomo Zalman Auerbach and the Chazon Ish held that one could use grape juice (Haggadah of Rav Shlomo Zalman Auerbach).
- Sh"t Mishneh Halachot 10:87, Nefesh HaRav (p. 185) in name of Rav Soloveitchik
- Rama 474:1
- S”A 474:1
- Halichot Shlomo 9:24
- The Mishna (Pesachim 117b) states that it is permitted to drink wine between the 4 cups of wine, except between the third and fourth cups. The Rashbam (108a s.v. Bein Shelishi) explains that one may drink wine between the first, second, and third cups because it serves as an appetizer for the Matzah. However, after Birkat HaMazon, when there’s no more need to eat Matzah, drinking an extra cup appears as though one is adding on to the established 4 cups of wine. See Reshimot Shiurim (Sukkah p. 139) for an explanation of why it only appears as adding but does not violate Bal Tosif.
- The Yerushalmi (Pesachim 10:6), however, explains that one should not drink between the third and fourth cups so as not to get drunk, which would prevent a person from saying Hallel. Drinking between the earlier cups is not an issue because during a meal, wine is not as intoxicating.
- Rambam (Chametz U'Matza 7:10), Tur, and S”A 473:3 and 479:1 codify the Mishna. Mishna Brurah 479:5 writes that based on the Yerushalmi, one also may not drink any intoxicating drink, and as a stringency according to the Rashbam, one may not drink Chamar Medina (which is valid for the 4 cups).
- S”A 473:3 writes that even though it’s permitted to drink but one should be careful not to drink too much wine so as not to become intoxicated and become unable to finish the Haggaddah. Darkei Moshe and Mishna Brurah 473:14 write that such is our minhag.
- Mishna Brurah 473:13 writes that according to Ashkenazim that make a bracha on each cup of wine and making a bracha on wine unnecessarily is forbidden because it looks like one is adding to the established number of cups of the night. Therefore, if the wine was on the table as one made the bracha or one had intention to cover anything that comes later, it’s permitted to drink the cups.
- Mishna Brurah 473:16
- Mishna Brurah 473:12
- Kitzur Shulchan Aruch 119:9
- Shulchan Aruch 472:8
- Shulchan Aruch 472:7, Yalkut Yosef 472:13
- Rama 472:7 writes that if one forgets to lean, he must only repeat for the first two cups. Mishna Brurah (472:21) notes that in general one should not repeat the first cup because doing so will require one to make another berakhah. Preferably, one should have in mind that one may drink in between the first and second cup and then if one drinks the first cup without leaning, one would be able to drink it again without a berakhah.