for your invacation question: you don’t have to say ‘ask smartthings’, what I say now is ‘alexa turn on [name of the device as listed on your smartthings app]’
[I think I misunderstood earlier question] by ‘ask alexa’ you mean the ‘ask alexa’ smartthings app? if so than nevermind invocation would be needed, I dont’ use the ‘ask alexa’ smartthings app, I use the built in integration so invocation is not neeeded]
if the name is fairly unique you don’t have to say the complete title, e.g. kitchen light with dimmer, if you only have have one device named ‘kitchen light with dimmer’ you could just say you could say ‘alexa turn off [light]’ but if you have multiple items such as entrance light, backyard light, stairs light, etc then you need to be more specific, alexa turn on [backyard light]
to do and commands grouping as metioned works…also consider using Echosistant
checkout the youtube demo [DEPRECATED] EchoSistant Evolved ~ Amazon Echo's Only Assistant with Robust Scheduling and Flexible Reporting