1. If there is no stay by the high court, then the pendency of the writ will not have an impact, however you can make an application before the concerned authorities stating the matter is pending before high court in the writ petition No....... hence to adjourn the decision of acquisition of the properties till the disposal of the writ petition, the collector may certainly pay heed to this application, if necessary you may attach a photo copy of the writ petition for the information of the authorities.
2. You cannot take illegal possession if the possession is already there with the authorities in the name of acqusition.
As per land acquisition act, they can take possession by just giving you notice and would suitably compensate you as per the prevailing law.
So your act of taking possession would not be of any use to you.
3. Instead of taking possession, you can file a mandatory injunction suit against the authorities restraining them from acquiring the property forcibly before making the settlement of the compensation amount.
4. It depends, because you and the opposite party are the people involved in the negotiations, hence you should be knowing it better, you dont agree for the unjustified compensation.
5. There may not be any contempt in this case, if the stay is vacated, hence you confirm the latest position on this. You can block the access road so that the authorities will once again come for talks, but dont budge to any pressure, you may dictate terms for fair compensation and it is feasible you may withdraw everything and settle down peacefully.