I will put all these on the same page.
1) If a niddah stops at day 3 and has 7 clean days, is she permitted?
2) Once a zav immerses, is he permitted to his wife but not to terumah or kodesh?
3) Can one be a zav today?
4) On day 7, can she immerse midday and be permitted to her husband? The notes to 33a say that Biblically she is permitted as "part of a day is like a day." Do we Rabbinically prohibit this?
Barry Epstein, Dallas, USA
1) No. One must generally wait five days before starting the seven clean days (see Remah Y.D. 196:11 and Mareh Kohen pg. 37).
2) He indeed cannot deal with Taharos, as we are scared that he will still see a flow before nightfall, ruining his seven clean days and rendering him retroactively Tamei. However, I do not know of any source offhand that prohibits a Zav from being with his wife even while Tamei, although his wife would obviously become Tamei as she is considered as touching a Zav (see Rambam Mishkav u'Moshav 3:3 who states that one who has relations with a Zav has the same Halachic Tumah as someone who touches a Zav, unlike one who has relations with a Nidah).
3) I don't see why not.
4) This is Rabinnically prohibited for the same reason given in answer 2) above (see 67b at length, and Shulchan Aruch Y.D. 197:3).
All the best,
Yaakov Montrose