I bought a used car battery from Auto Zone for $20 just to get mine running and then added a deep cycle marine battery. I keep the spare car battery charged and use it onboard for my radio and added a lighter socket for my cell charger, spotlight or whatever I may need without drawing my other. It also gives me a spare if I need it. Battery cables are just like car types so just measure the length you need and buy it at an auto store. Just to be honest. If your sweating the price of a battery cable,(under $20) you might not want to tackle such a large project. Just hate to see anyone get deep in their pockets and end up with a pile of parts they have to lose money on..
Best case scenario you'll have a few hundred in the motor before it is reliable,
Carb rebuilds,points and condenser,plugs,fuel lines,fuel pump and filter,water pump,thermostat(if equipped),service lower unit and possibly seals,battery,gas,oil, fueltank...not unususal to have a bad coil or 2 when they sit a long time. Starter is another concern from sitting. easily $400-600 in parts alone.
I don't want to discourage anyone, just sharing my personal experiences. Sometimes you find a gem but usually your working with rocks..LOL
Keep us updated and as I said, I'll help where I can !!