Restore a boat 1st steps? Motor? Need advice

Dad and I bought an old boat to restore. Its a tri hull with a Chrysler 105 HP motor that supposedly works. The compression is good. To start it we need to get a key made and connect the throttle and steering cables I believe. Also the gas tank and line. Are throttle and steering cables universal? If not how hard will it be to get those for a '73 Del Magic and where do you get them. Online or a local boat place. This is our first project and we are new to this in general but we got a good deal. After the motor i believe we can do the lights and rails and floors and seats and so on but I believe the motor is the first thing we should tackle. Any advice for some newbies.

Before you dive too deep into what could be a bottomless pit, you need to do a little testing.

Plastic or rubber mallet, tap around the transom and under the hull. You must hear a nice solid tap sound, if you hear a thud, that is a waterlogged (rotted) place. Same thing on the decks and floors, any boat of that vintage will have wood decks and floors, and depending on where it lived will have a fairly high chance of needing replacement.

Ebay is gold for finding used parts.
Steering is generic, throttle/shift cables must have the chrysler connections to work.
Any generic key switch can work.
Fuel lines are a given, they'll be junk.
Fuel tank? Put a rag on a stick and wipe around, if you come back with a stick full of goo, you have problems.
Good luck with it, not sure what you've got to spend but free boats are usually very expensive.

Thanks for the advice I'll take it one step at a time. We don't have a lot to spend but we are hoping over time we can slowly get it going. We will check the floors for soggy foam under the wood and any standing water. Thanks. My Dad is freaking out about it now that its home and such a big project. We have a smaller boat to fish out of until its done. Its a tri hull '73 Del Magic(the project boat). It'll be a fun boat if we can accomplish our goals.