3 Re-rolls should be enough for a starter Vampire team. I generally stick to the rule - do not have more vampires than re-rolls. Starting with 2 Grave Guard gives you a solid wall of Block which should help reduce the number of Re-rolls you are using. 5 Thralls and 3 Zombies means you have 13 players which is useful for attrition and 3 zombies are perfect for LoS duty. 3 Vamps is a safe number and as they start with MB you should be able to win the battle of attrition quite easily at rookie level even though you can't have an apothecary and you will be hurting your thralls from time to time.