[RPG] combine Haste, Green Flame Blade, Divine Smite, and Thunderous Smite like this

This is a perfectly valid use of Divine Smite and a smite spell

We can see in the description for Divine Smite that the attack must be a melee weapon attack:

Starting at 2nd level, when you hit a creature with a melee weapon attack, you can expend one spell slot to deal radiant damage to the target, in addition to the weapon’s damage. [...]

We don't have any additional restrictions on the use of Divine Smite, other than that we must have a spell slot to expend.

The various Smite spells available at time of writing (Banishing, Blinding, Branding, Searing, Staggering, Thunderous, Wrathful) all begin with a variant of the following:

The [next] time you hit [a creature] with a melee weapon attack...

There is not a restriction saying you cannot combine these two effects. So, given they meet all requirements (a melee weapon attack and a spell slot to expend), a paladin could indeed use both a smite spell and the Divine Smite feature on a single attack.

We can also look in the Sage Advice Compendium for further clarification:

Can my paladin use a smite spell along with Divine Smite? As in, I cast wrathful smite, hit, then use Divine Smite on the same attack?

Yes, you can use Divine Smite on the same weapon attack that benefits from a smite spell, such as wrathful smite—as long as the attack you make after casting the smite spell is a melee weapon attack. Divine Smite doesn’t work with any other kind of attack.

While this is certainly powerful, it is also resource-intensive. A low-level paladin choosing to do this might struggle to perform during the rest of the adventuring day.

Yes, they stack perfectly well.

Neither ability requires an action to use, so as long as you hit with a melee weapon attack that happens to use your pact weapon you can use both. The only exception is that Eldritch Smite can only be used once per turn, while Divine Smite can be used as many times as you have melee weapon attacks.

If the intent was to use only one at a time it would be called out in the text or require a bonus action or something else that is clearly not the case here.