Automatic Top-off help

[teatimecrumpet]

Hi, I'm new to NR and want to start off by saying thank you and looking forward to helping where I can and soaking up all the available knowledge!

I'm looking to build an ATO using a 12VDC relay, a float switch, and an extension cord for an air pump to a sealed reservoir. I just have a couple of questions before I buy the parts on ebay.

 

• I noticed that the relays I keep finding show 2 of the 8 pins offset one on each side.  The ones I've seen in the guides and from kingofdiy on youtube show them aligned in perfect squares.  Am I missing something or is it the same in just a different layout
  • https://www.ebay.com/itm/12VDC-Coil-Power-Relay-10A-DPDT-LY2NJ-HH62P-L-JQX-13F-2Z-with-PTF08A-Socket-Base/372497925221?hash=item56ba9b4465:m:m6tI55ExbILUQP5twtNrSdg:rk:3:pf:0
• Which is better air pump or water pump? I chose an air pump over a pump because I'd rather an air pump run dry and break than an overflowing tank (though I'm thinking I'm going to put a float switch in reverse in the reservoir maybe or in reverse at the top of the tank).  
• Is there a limit to what I plug into the modified extension cord in terms of wattage?
• I noticed the guides mention getting DC vs AC equipment when the relay is going directly into the equipment but since this is going into the extension cord do I even have to worry about that?
   

Thank you all!