This should cover most items unless you wish to read the topic at the head of XP Forum area.
Will microsoft continue to host the patches and service packs for XP after 4/8/2014? <- These will exist in the archives for a few more years, plus privately hosted samples as we all have saved samples in our private backups, to re-install if needed.
Would the automatic downloads work? <- There are no automatic downloads unless you have a Private Antivirus / Antimalware program that downloads. Nothing from Microsoft. Even Microsoft Security Essentials (M.S.E.) will no longer be supported.
Would we need to manually download them? <- You will manually download except for similar private items mentioned above.
What happens if one would like to re-install the software after that date? <- You can still install / re-install XP after the date.