OK, if you don’t want to mess with testing, go for the lemon cake in 6” and 9” or else the downy yellow in a 12” (Cake Bible, wedding section). The 12” will give a few more servings. Sorry, I’m not really experienced enough with larger crowds to advise you on serving size, but if you start out with smaller pieces cut in concentric circles you’ll probably be fine.
To scale Woody’s Lemon Lux cake, the maximum I came up with was 1.46x, so if you go to 1.5x (multiply everything by 1.5), perhaps make a cupcake or two. According to the pan capacities, you only need to go up about 1.1x, but in the Cake Bible it says you can scale up by a third for 2” high pans, and then adding another 10% for the 6” pan gives the figure I mention. You may need to extend baking time to account for the deeper layer, be sure to check doneness before removing the cakes from the oven. And check to see that the pans will all fit in your oven in one go. If not, you could put the larger pans (filled, don’t leave the batter in the bowl) in the refrigerator while the smaller pans bake.
For the strawberry cloud cream, you’ll need to have a minimum of 1.5 cups for one layer of filling between the two layers of both the 6” and 9” cakes, triple that if you’re going to torte the cakes.
For the buttercream, I would not chance it with non-dairy white chocolate. Not sure what to say as most every cake frosting has dairy, especially any that would be appropriate for an upscale strawberry shortcake! Perhaps you could bring something else for the dairy-intolerant partygoer. I also would not chance the cake without real white chocolate and real butter.
The only cake that doesn’t have dairy is the biscuit de savoie or the chiffon. You could make the lemon version of the orange chiffon layer from RHC in place of the butter cake. But if it were me I would just bring something else rather than mess with dairy substitutions.