Control horizontal and vertical space in grid.arrange with sliders in shiny app

I need to create a shiny app in which the user decides how many charts to display and in how many columns via sliders.
To merge the graphs I used the function grid.arrange but it is not mandatory, the important thing is to have ggplot objects. And I need coord_fixed().
This is a small executable example:

library(shiny)
library(shinythemes)
library(readr)
library(ggplot2)
library(dplyr)
library(tidyr)
library(grid)
library(gridExtra)
library(ggforce) 
library(shinythemes)

ui <- fluidPage(
 
    navbarPage("MotorBrain", 
               
      tabPanel("Configurazione",
               sidebarLayout(
                   sidebarPanel( 
                      sliderInput("input1", "N. utenti",
                                    min = 1, max = 133,
                                    value = 3),
                       sliderInput("nCol1", "Ncols",
                                    min = 1, max = 32,
                                    value = 1),
                       actionButton("goButton1", "Visualizza")),
                       fluidRow()))),
      tabPanel("Visualizzazione", 
            fluidRow(
                   uiOutput("outputTest1"))
               
 ))




server <- function(input, output,session) {
    
 input1<-eventReactive(input$goButton1,{
        input$input1
    })
output$outputTest1 <- renderUI({ 
pl <- vector("list", length =  input1())
                        
for(t in 1: input1()) {

      p<-ggplot() +
         geom_point(x=runif(10000,0, 1),y=runif(500,0, 1))+
         coord_fixed()
                             
 pl[[t]] <-p
                         
 }
                        
output$plot_test1<- renderPlot({
                    
 grid.arrange(grobs=pl,ncol=input$nCol1,top="")
                                
  })
                        
plotOutput(outputId = "plot_test1")
                        
 })                 

}

shinyApp(ui = ui, server = server)

I need to add two more sliders with which the user can decide how much horizontal and vertical white space to put between the various graphs in the grid.
How can I do this?