Can anyone tell me the size of the bolt I need for the upper alt bracket? This is the bolt that goes into the head right under the valve cover.

Also, what is used to seal off the coolant line on the block that is no longer used?

The bolt is a 10mm x 20mm , It will have a 14mm head which is a common size on your Honda.
To Block off the hose you don't need, The best way is to have it welded. The other way is to buy a coolant plug ( not vacume) and use a hose clamp.