TThread one instance at a Time

Question

I need a single background thread for my application . If triggered it will simply do some queries against a SQL Database and update another Table . For the sake of simplicity I built myself a Test project to test out my idea . And I came up with the following code :

unit uMain;

interface

uses
  Winapi.Windows, Winapi.Messages, System.SysUtils, System.Variants, System.Classes, Vcl.Graphics,
  Vcl.Controls, Vcl.Forms, Vcl.Dialogs, Vcl.StdCtrls;

type
  TBackGroundThread = class(TThread)
  protected
    procedure Execute; override;
  end;

type
  TMain = class(TForm)
    Memo1: TMemo;
    btnStartThread: TButton;
    Memo2: TMemo;
    procedure btnStartThreadClick(Sender: TObject);
    procedure FormCreate(Sender: TObject);
  private
    { Private declarations }
    var
    BackGroundThread : TBackGroundThread;
    SafeToStart : boolean;

    procedure ShowID;
  public
    { Public declarations }
  end;

var
  Main: TMain;

implementation

{$R *.dfm}

procedure TBackGroundThread.Execute;
begin
  Main.SafeToStart:=false;

  Main.ShowID;

  Main.SafeToStart:=true;
end;

procedure TMain.FormCreate(Sender: TObject);
begin
  SafeToStart:=true;
end;

procedure TMain.ShowID;
var i : integer;
begin
  for i := 0 to 10 do
  begin
    sleep(100);
  end;


  Memo1.Lines.Add(IntToStr(BackGroundThread.ThreadID));

  Main.SafeToStart:=true;
end;

procedure TMain.btnStartThreadClick(Sender: TObject);
begin
  if SafeToStart = true then
  begin
    BackGroundThread := TBackGroundThread.Create(false);
    BackGroundThread.FreeOnTerminate:=true;
  end
  else
  begin
    Memo2.Lines.Add('OOPS' +IntToStr(BackGroundThread.ThreadID));
  end;
end;

end.

I am using Private Global Variable to check if it is OK to start or not , I thought this should be safe because I only have one Background task. The Execute will be inside a try except end block.

I tried to check if I have memory leaks , but Delphi did not report any.

My question is :

if I set the FreeOnTerminate property to true, then after the execute the Thread will automatically free itself ?

Thank you.

UPDATE 1

As for the VCL Manipulation from within the thread I will use this :

TThread.Synchronize(TThread.CurrentThread,
procedure
begin
seriesQM.AddXY(qryStat.FieldByName('CurrentPeriod').AsDateTime,qryStat.FieldByName('GesCutQM').AsFloat,
            qryStat.FieldByName('Hour').AsString,$00FF9F40);
end);