We start at level 2 and i want to do a combination of the two for my character. I was thinking either Fighter 1-3 Wizard 4-5 Fighter 6-end of campaign or Fighter 1 wizard 2-3 Fighter 4-end of campaign or Fighter 1-5 wizard 6-7 then fighter 8-end of campaign. But im open to other levelling options, or advice on if the build is viable or not.
So, why Echo Knight vs Eldritch Knight if you want only a slight dip into Wizard? What is your real interest in the Bladesinger subclass? You do know you are limited to a one-handed weapon, no shield and only light armor to be able to use the Blade Song feature right?
I assume you'll play a dex-based light armored duelist type of fighter with a rapier? Your Echo Knight class abilities use your CON for the DC, this means you'll need high DEX, CON and INT to make the best use of this multiclass, this seems quite MAD (multi-ability dependant) to me.
An Eldritch Knight would not only grant you 1/3 of your fighter class levels towards allocating you with more spell slots but its DCs and spell casting ability are tied to your INT which synergizes well with the Wizard class. Of course, you'll still need good DEX and CON if you want to fight up close but your CON won't directly affect your class features, only your ability to stay in a fight so it won't be as important to pump it up and you can focus more on INT and/or DEX.
P.S.: Have you considered a Battle Smith Artificer/Bladesinger multiclass instead to be more SAD? Battle Smith is a pretty strong half-caster that gets a ton of neat features including the ability to use INT to their atk/dmg rolls. This would mean you only really need INT/CON and nothing else.
Personally, I'd stick to a pure Echo Knight fighter, no multiclass or multiclass into another martial class. Barbarian maybe? Path of Wild Magic is a fun one if you want something magic-like and all its abilities also scale off of CON which would synergize well with the Echo Knight's class features. One of my friends is playing one and loves it. This would also not limit you to light armor/one-handed weapon/no shield.
If you REALLY wanna make a bladesinger, I'd either go pure 20 levels of Wizard bladesinger or at most start with a 2 level dip in fighter instead if all you want is Action Surge and proficiency in Con saves and don't pick up an archetype. Alternatively, a 3-level dip in Artificer Battle Smith will give you that sweet INT to hit/dmg I mentioned, proficiency in con saves and still let you retain all the goodness of the Wizard class, including access to 9th level spells. You're still limited to light armor/no shield/one-hander to use the Blade Song feature though.
War magic is a decent alternative to blade singer that doesn't limit you into a particular equipment type and could synergize well with both Battle Smith and Eldritch Knight.
Edit: If you're really more about fighter then wizard, a pure Eldritch Knight is a force to be reckoned with, its alot more defensive then people think it is but your capstone is a 4th attack. A 15 Eldritch Knight/5 Blade singer would also work. Let you get 3rd level Wizard spells, gets most of the nice features from the Blade Singer subclass and you stop just before the extra attack feature that's useless to you since you already get 3 and you still get Eldritch Strike and Arcane Charge which are amazing. This would give you as many spell slots as a 10th level Wizard so 4/3/3/3/2 instead of the 4/3/3/1 you'd get as a pure Eldritch Knight. Much better then the puny 3x1st level slots you get from the Echo Knight/Bladesinger which only gets slot from Wizard.
If I wanted to do this, I'd probably go Figher 1-5 -> Wizard 1-2 -> Fighter 6-15 -> Wizard 3-5. Fighter 1-11 -> Wizard 1-2 -> Fighter 12-15 -> Wizard 3-5 would also work but if you're going to take the wizard levels so late anyway, why bother multiclassing at all?
We start at level 2 and i want to do a combination of the two for my character. I was thinking either Fighter 1-3 Wizard 4-5 Fighter 6-end of campaign or Fighter 1 wizard 2-3 Fighter 4-end of campaign or Fighter 1-5 wizard 6-7 then fighter 8-end of campaign. But im open to other levelling options, or advice on if the build is viable or not.
So, why Echo Knight vs Eldritch Knight if you want only a slight dip into Wizard? What is your real interest in the Bladesinger subclass? You do know you are limited to a one-handed weapon, no shield and only light armor to be able to use the Blade Song feature right?
I assume you'll play a dex-based light armored duelist type of fighter with a rapier? Your Echo Knight class abilities use your CON for the DC, this means you'll need high DEX, CON and INT to make the best use of this multiclass, this seems quite MAD (multi-ability dependant) to me.
An Eldritch Knight would not only grant you 1/3 of your fighter class levels towards allocating you with more spell slots but its DCs and spell casting ability are tied to your INT which synergizes well with the Wizard class. Of course, you'll still need good DEX and CON if you want to fight up close but your CON won't directly affect your class features, only your ability to stay in a fight so it won't be as important to pump it up and you can focus more on INT and/or DEX.
P.S.: Have you considered a Battle Smith Artificer/Bladesinger multiclass instead to be more SAD? Battle Smith is a pretty strong half-caster that gets a ton of neat features including the ability to use INT to their atk/dmg rolls. This would mean you only really need INT/CON and nothing else.
Personally, I'd stick to a pure Echo Knight fighter, no multiclass or multiclass into another martial class. Barbarian maybe? Path of Wild Magic is a fun one if you want something magic-like and all its abilities also scale off of CON which would synergize well with the Echo Knight's class features. One of my friends is playing one and loves it. This would also not limit you to light armor/one-handed weapon/no shield.
If you REALLY wanna make a bladesinger, I'd either go pure 20 levels of Wizard bladesinger or at most start with a 2 level dip in fighter instead if all you want is Action Surge and proficiency in Con saves and don't pick up an archetype. Alternatively, a 3-level dip in Artificer Battle Smith will give you that sweet INT to hit/dmg I mentioned, proficiency in con saves and still let you retain all the goodness of the Wizard class, including access to 9th level spells. You're still limited to light armor/no shield/one-hander to use the Blade Song feature though.
War magic is a decent alternative to blade singer that doesn't limit you into a particular equipment type and could synergize well with both Battle Smith and Eldritch Knight.
Edit: If you're really more about fighter then wizard, a pure Eldritch Knight is a force to be reckoned with, its alot more defensive then people think it is but your capstone is a 4th attack. A 15 Eldritch Knight/5 Blade singer would also work. Let you get 3rd level Wizard spells, gets most of the nice features from the Blade Singer subclass and you stop just before the extra attack feature that's useless to you since you already get 3 and you still get Eldritch Strike and Arcane Charge which are amazing. This would give you as many spell slots as a 10th level Wizard so 4/3/3/3/2 instead of the 4/3/3/1 you'd get as a pure Eldritch Knight. Much better then the puny 3x1st level slots you get from the Echo Knight/Bladesinger which only gets slot from Wizard.
If I wanted to do this, I'd probably go Figher 1-5 -> Wizard 1-2 -> Fighter 6-15 -> Wizard 3-5.
Fighter 1-11 -> Wizard 1-2 -> Fighter 12-15 -> Wizard 3-5 would also work but if you're going to take the wizard levels so late anyway, why bother multiclassing at all?