What's your starting procedure Malby?
Check to see if you have choke plates or an enricher device. If choke plates, when you press the choke button you will here a click and see the choke plates cover the carby throats (cowl off of course).
If choke plate model proceed as follows:
1) raise warm up lever to 3/4 height or thereabouts
2) hold key pushed in to activate choke and keep held in whilst cranking. It is only choking whilst the key is held in.
It should fire within a couple of seconds. When it does quickly bring the fast idle lever back down a bit so it doesn't rev it's tits off. If that stalls it then repeat the process. Work the warm up lever to keep it at a fast idle for around 30 seconds then you should be able to drop the lever all the way down.
If an enricher model the procedure is very similar except that the enrichener works like a bucket with a hole in it. Press and hold the key to activate the enricher. Hold it down for 5 seconds BEFORE releasing and then cranking. The 5 seconds allows the enricher device to drain one of the carbs float bowls into the crankcase.
The cold telltale is not a concern.
There is no thermostat in your engine per se. The block has restrictor holes in the outlet that control the flow rate of water exiting the block, hence acting as a thermostat.
Oil leaking down the leg I wouldn't be too concerned about as mentioned. What it needs if it's been owned by an old codger is a nice big, hard, hi speed, flat knacker, screaming run! That's not a flippant remark but a genuine comment. Drain the fuel if it's old (older than 8 weeks) and put fresh fuel in using Quicksilver oil and take it for a hard long run.
Whenever I bought boats in for yard stock I always took them for a good hard run but would always stay close to shore. Like, 200m offshore and run for 5-10 k's down and then back. It's a good shakedown which will let you know how the engine performs, is it propped right and is the engine height right and are there any odd behaviors from the hull (eg: porpoising, burying the nose, heavy heavy steering pull etc)
You can run her dry (at idle) each tine you put her away if you like. Not really an issue if you use it regularly but it's fine to do that. Little bit old school though!
Cheers