the stock shock towers are good.....if you break one then get the rpm....
a 2 cell w the stock speedo....mmmmm you will be running at the limit of the esc (voltage wise) 2 things to do to the stock speedo 1 get the FT heatsink for it ($4) the next is the speedo can come apart after a hard hit (dont ask) so I started taping the seams on the sides of the speedo....
Now your speedo will be really good to go....
The lvc is always a good idea....
For a 5 year old I would make 4.8v packs....you can bias the weight to the rear so it will jumpo like a champ and it will not have that plastic shattering speed....

w 4 2/3a cells you can gear up to make it faster it will not be a total pig....