I'll try
1.- Taos can't hold two weapons, zhey do not have second weapon slot at all. Not even with hacks (these works for other classes but not for taos).
2.- Most of the time it's better to use XP *****. I would search official forums for calculations, but search does not work. I remember there was one level for which was better to use DBs, but it's 129 or was it 121 (sry, I don't really remember).
3.- Do you mean by being plvled from 135 archer? Because 135 is max level and you can't get XPs with such char. Also depends on level of plvled character, SRGs and monsters.
4.- I don't think so, never heard of it.