Formatting Shiny Plotly subplots - Individual titles and graph size

I'm trying to provide individual titles for each of my graphs within plotly's subplot function and I found a post where you can extend subplot using %>% layout(title = "Main Title) but I'd like individual titles for each graph (I'm using ggtitle but that only plots the last title provided (Plot 4). I found a similar post Provide title to each of the subplots - R Shiny but I don't think that I can facet_wrap in my scenario.

Furthermore - I was wondering how to increase the margin between the graphs in a subplot since they seemed to be really squished together.

Any help appreciated!

ui <- fluidPage(
  sidebarPanel("This is a sidebar"),
  mainPanel(plotlyOutput("myplot"))
    )

server <- function(input, output){

  output$myplot <- renderPlotly({

    gg1 <- ggplotly(
      ggplot(iris, aes(x=Sepal.Length, y=Sepal.Width)) + 
        geom_point() +
        theme_minimal() +
        ggtitle("Plot 1")
    )

    gg2 <- ggplotly(
      ggplot(iris, aes(x=Species, y=Sepal.Length)) +
        geom_boxplot() +
        theme_minimal() +
        ggtitle("Plot 2")
    )

    gg3 <- ggplotly(
      ggplot(iris, aes(x=Petal.Width)) +
        geom_histogram() +
        ggtitle("Plot 3")
    )

    gg4 <- ggplotly(
      ggplot(iris, aes(x=Petal.Length)) +
        geom_histogram() +
        ggtitle("Plot 4")
    )

    subplot(list(gg1,gg2,gg3,gg4), nrows = 2)
  })
}

shinyApp(ui = ui, server = server)