1.6 About the drains is simply asking you not to put things down the drains that may block them. This is because it will cost to get a plumber to come and clear them. If you use normally and don't put things that should not be put down the water drains then there will be no problem.
1.16 is just saying the flat must be heated. Sometimes if people don't heat the flat or put the hot water on in winter then the water pipes freeze and burst. This will not happen with you because you will be heating the flat. No?
1.17 is asking you not to use any form of heating that uses paraffin because this is dangerous and catches fire. Is the flat centrally heated? If so then use the central heating. Sometimes people want to save money so but cheap heaters that use paraffin and this is dangerous so he is asking you not to do it.
1.24 is saying if the landlord get letters that come to the flat you must give them to him or take them to the letting agent so that they can give them to him.
3 is saying the landlord will decide what state the flat is left in when your contract finishes and you leave the flat. They always say this to protect themselves but as I said in the last e-mail, make sure you take pictures before you move in and any damage is reported to the landlord so that he accepts this before you move in.
4.2 is saying you have right to live in the flat without the landlord or agent disturbing you - they are agreeing to give you privacy and peace in the flat.
Page 4 is just stating that the landlord can use the deposit to cover cost for repairing or cleaning the flat is you leave it in a bad state. Just make sure you clean the flat when you leave and don't damage anything otherwise he will use your deposit to put things right.
5.4.3 and 5.4.4 is saying if there is a problem and you have a complaint about the landlord taking your deposit your have to put this in writing within 30 days to the landlord and ICE. If you don't do it within 30 days then they may not accept your complaint. If you make the complaint within 30 days and the landlord does not satisfactorily resolve the issues you can report him to the ICE. This is just legal stuff to protect you but hopefully it will not get to that.
A13 is saying the landlord or agent must register the deposit you have paid with the Deposit Protection Service to say they have received this and are keeping it as part of your agreement. They should give you proof that they have done this within 30 days of giving them the deposit so that you know it is safe. If they don't give you proof you can ask for this or even report the landlord, This is also to protect you and make sure the landlord does not steal your deposit.