In addition to what Crosbyman’s good advice, what you have already planned to do; there are some grease fittings on and near the transom clamps to lubricate the tilt and pivot hinges. Since you have a boat with a steering wheel, make sure the steering tension adjustment on the motor is adjusted loose. Clean or put in new spark plugs. Make sure the gas tank is clean and the fuel line and connectors are in good shape. Old fuel line connectors have a O-ring seal inside that gets had and leaks. New connectors are readily available, but beware of metric connectors that look much the same made for Yamahas and some Mercurys.
Did you get a wiring harness with solenoid box, ignition key switch, and choke switch for the motor? It plugs into the starboard side. Note the motor will rope start without all that if there is no harness plugged in, as the key in the off position shorts the points together, so if it’s not there, the motor will start by rope. If you need a harness, check E-Bay and Craigslist and/or post a “Wanted” ad on the classified board here.
Your Crestliner looks like a Voyager14, which should have the nice splashwell in back. The snaps on the windshield indicate it originally came with a convertible top. Great that you have your Grandpa’s boat! My Dad bought one of those new in 1958 when I was 11 years old. He traded it in 1984. About 5 years ago I bought another one like it. Your boat originally would have had a red hull and decks with sides above the splashrails painted gray. Gray inside also above the floor. 1958 was the first year of the Crestliner Flying Crest logo sticker on the sides. There used to be a good retrocrestliner website for restorers, but it went down many months ago. There is a facebook site called “Vintage Crestliner Boats” that you can join.
This site link will get you to remnants of the old retrocrestliner site that still exist on the web, but not everything you click on will be there: https://web.archive.org/web/20190421202623/http://www.retrocrestliner.com/
That boat will do well with that 35 Johnson. I have run 30, 40, and V4 60 HP on Dad’s old boat and now have a 40 on my current Crestliner. It’s rated for 60, but the weight of the motor screwed up handling some. I think 35 – 40 HP is ideal. It’s a light boat so you will want a high pitch prop, unless you are carrying heavy loads most of the time.
Dave
Here is my current boat with a 1959 35 Lark – 1957, but same boat, except no convertible top snaps and 1957 logo on the side: 
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