Welcome to the forum. I'm not sure I understand what the slats would be on an airdeck? But if it is missing a floor - you can make one if you have the skills. Finding affordable marine ply might be the challenge.
2nd hand outboards are a bit of a gamble, especially if you are new to the game. Personally I wouldn't buy one of the less reputable brands because getting parts for them or tech support can be hard if something goes wrong. Whilst outboards do sometimes fail unexpectedly (and so make sure you have a back-up plan and good comms), most often they probably die ashore. I think the cheaper engine brands are typically bought by people who want the reassurance of a new engine and are willing to forfeit resale value when it comes. If you buy one new, look after it well and only hope to use it for say three years they probably are fine. Most of us see them as longer term investments.
If I was looking for 2nd hand in your neck of the woods I'd ideally want it to be somewhere with some come back if it dies after a month. Clyde Outboards in Greenock sold me a 2nd hand o/b and found and fixed a gremlin in it for me quickly, but are probably in the more expensive end of the 2nd hand market (along with Yampower, Bosun's locker etc if they have anything in stock). Davie Anderson in Tayport has probably the best reputation in Scotland for random o/b bits and has occassionally posted on here in the past. Less well known is a guy who works from a farm at Ratho (or he did last time I was there which was pre-covid) - if you don't know who I'm talking about I'll dig around and see if I can find his name / number.
The one possible exception to the known brands only rule might be Selva - who are less known here but I think have more of a following elsewhere and are essentially Yamaha based.
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