Tunnel Fighter + Oath of Vengeance + Echo Knight Potential Combo Ruling

Question

I was thinking of a new character and had a question about how this would work. You are a Echo Knight (Level 3+) Multiclassed with a Oath of Vengeance Paladin (Level 7+) who has the Tunnel Fighter fighting style (from this UA) and has used their bonus action to activate it on your turn. You and your Echo stand within 5 feet of a creature and it provokes an opportunity attack.

1. Would both you and your Echo get an opportunity attack since your reaction isn't used?
2. Could you then move up to the enemy who ran away getting within melee reach again?
3. Could your Echo do likewise and move up with you within melee reach of the fleeing creature?
4. Would you then both get to make an opportunity attack again if it leaves your reach (or just you if number 3 is not possible)?

I think you can't do this because you have to use your reaction the first time to move up to the creature. Could you repeat this again moving into the creatures melee reach?

'Tunnel Fighter (UA). As a bonus action, you can enter a defensive stance that lasts until the start of your next turn. While in your defensive stance, you can make opportunity attacks without using your reaction, and you can use your reaction to make a melee attack against a creature that moves more than 5 feet while within your reach.'

'Relentless Avenger. By 7th level, your supernatural focus helps you close off a foe's retreat. When you hit a creature with an opportunity attack, you can move up to half your speed immediately after the attack and as part of the same reaction. This movement doesn't provoke opportunity attacks.'

'Manifest Echo. When a creature that you can see within 5 feet of your echo moves at least 5 feet away from it, you can use your reaction to make an opportunity attack against that creature as if you were in the echo's space.'

Answer 1

Some of this works, some doesn't

1: Two opportunity attacks

Both can make an opportunity attack since you don't need your reaction. Also it seems that you can have the echo make an opportunity attack because

use your reaction to make an opportunity attack [...] as if you were in the echo's space

This clearly defines the attack as opportunity attack and has you make it as if you were there, so I say that Tunnel Fighter applies.

2: Follow the opponent

Yes. If you hit with the opportunity, you can follow the opponent. You even get two chances because you make two opportunity attacks. Of course this depends on how far the opponent moves. You can only move half your speed so it is entirely possible that the opponent outruns you unless you have something that increases your movement. As for the reaction, the text is indeed unclear but I would say you can move without using your reaction. Relentless Avenger doesn't require you to use a reaction to make the opportunity attack because it says

When you hit a creature with an opportunity attack

it doesn't say anything about a reaction at this point. The overall text also makes it very clear that it is about hitting and then pursuing an opponent not specifically about making reactions. I would therefore argue that when the text later mentions a reaction you never used, you can simply ignore that part.

3: Have the echo move

This doesn't work. Relentless Avenger doesn't give your echo permission to move. Also (see 1 and 2) the echo doesn't make an opportunity attack.

4: More opportunity attacks

If for some reason the opponent moves again and your within reach (see 2), you can make another

Balance

You call this a combo but this isn't unusually powerful. First of all, the echo only gives you one extra opportunity attack. Multiclassing just for this seems like a very steep cost. Additionally, opportunity attacks only work, if an opponent willingly move out of your reach. So you're relying on your opponent to move. Having your opponents move out of your reach every turn or even multiple times per turn seems unlikely.