You don't necessarily have to have any monsters in attack position. The monsters you use for the Synchro Summon can be in defence mode, that doesn't matter. What matters is that they are face-up, because you can't use face-down monster for a Synchro Summon.
Monsters can only 'manually' change battle position in your main phases. If you want to change them during the battle phase, you will have to do it by a card effect.
Ultimate Tyranno's effect forces you to attack all of your opponent's monsters with it FIRST. Meaning, if it is in Attack Position, at the beginning of your Battle Phase, it must be the first monster that you attack with, and it must attack all of your opponent's monsters, once each.Because of this, Ultimate Tyranno's effect is not essentially "activated". It has a "continuous" effect, meaning that the effect takes place the second it hits the field. So in answer to your question, it is not a matter of whether you CAN, it is the fact that you MUST utilize its effect during each of your Battle Phases, as long as it is on the field in face-up Attack Position.
during the battle phase
Yes, of course. There's no reason to think he can only attack monsters that were present at the beginning of the battle phase, or before his first attack is declared. If monsters are summoned during the same battle phase, by any effect, he may attack them.
Yes, that is allowed. You cannot, however, attack and then change to defense in the same turn.
Yes, because it is a quickplay and can be activated during the battle phase.
Yes, if you control a monster in defense mode and it is changed to attack mode during the Battle Phase by a card effect, it can attack. The "Zero Gravity" Trap card is an example of a card that can switch your monsters' battle position during the Battle Phase. But if the monster already attacked that turn, was switched to defense mode, then changed to attack mode again by an effect, it cannot attack again on that same turn.
No it can not. "Cyber Dragon" + "Cyber Dragon" + "Cyber Dragon" A Fusion Summon of this card can only be conducted with the above Fusion Material Monsters. During battle between this attacking card and a Defense Position monster whose DEF is lower than the ATK of this card, inflict the difference as Battle Damage to your opponent. ^^It doesn't say it can attack 3 times.
If this card attacks a defense position monster your opponent controls, destroy all defense position monsters your opponent controls after damage calculation. During your end phase, destroy all of your monsters that did not declare an attack this turn.
No, you cannot attack your monsters on your side of the field.The exception to this rule are the cards Magical Arm Shield (MAS) and Ancient Lamp. If your opponent activates MAS, they will take control of 1 of your face-up monsters, except the attacking monster, and it is attacked instead. Ancient Lamp can make 1 your attacking monster attack another monster on your field instead.
When monsters attack during the Battle Phase, there are actually multiple "steps" that take place. When a player declares an attack, you enter the "Battle Step". If no card effects are activated that would stop the attack, you enter the "Damage Step" in which face-down monsters are flipped face-up and you actually calculate how much damage is done. It's at this point that a card that reads "during damage calculation only" can be activated or takes effect. For more information on how card effects can work and activate during the Battle Phase, refer to the Related Links section below.
There's no hard limit. Each of your monsters can attack once unless they've got effects that let them declare more, however as long as you can keep replacing your monsters with new ones without ending the battle phase, these can all declare attacks too.