Any place that sells batteries can tell you the correct size to buy.
Mercury 1984 6 cylinder L6 what type & size of starting battery is required
550 cca
The 75 hp Mercury outboard will need a starting battery in the 650 CCA range, although, up to 1000 CCA would work just fine.
For a 2005, Mercury 3.3 hp outboard, a NGK BPR6HS.
Mercury wants you to install a battery with at least 525 marine cranking amps if you boat in the summer, and 1000 marine cranking amps for winter boaters.
1 gauge cable should do the job
For a 2 stroke model, a 500 to 650 cca, 12 volt starting battery will be sufficient. The recommended battery for a four stroke model is 1000 cca,
OD281588
Depends if it fiberglass or Aluminium. For Fiberglass you would be looking at around 50hp-60hp and and Aluminium would be between 30hp and 40hp.
1-1/2x16
36R
The 2002 model, 60 hp Mercury outboard requires an NGK BP8H-N-10 spark plug, the gap set to .040in.