You can use the same chain for 5-8 speeds.
The cheap chain tools from the box stores will work for awhile IF you are careful and separate/join the chain in small steps, resetting/aligning the tool each time.

A 53" chain should be 106 links. Best to see how to properly size a chain at the Park Tool website or elsewhere.
I wouldn't count on the chain on a Walmart bike being "properly" sized.
Your new chain will likely have to be shortened a few links.
DON'T shorten in the WRONG spot. You must have an inner link joining an outer link.

http://www.parktool.com/blog/repair-help