Maybe also look ip a good component library, for C# I use MudBlazor, which has great documentation that helps a lot to pick the right component for the job, and a lot of the hard work is already done in terms of styles/themes.

For my apps I use the MVVM pattern and write all the backend logic first, then that helps me narrow down the right way to display it.

Assuming this is C#, you could just make Reservation a record type, which can be defined with a one line primary constructor, is immutable and has value type equality. Second example is an insane amount of boilerplate.

For my sins I spend a significant part of my time maintaining smalltalk, and it most definitely is not productive.

The syntax is ugly and cumbersome when you start chaining messages. Any advantages the evangelists tout are available in modern languages without the baggage of this dead one.

Today if you want something ‘simple, flexible, interactive’ (interpreted, GC and likely faster) python would almost certainly be a better choice.