I know at level 15, one can get a weapon swap (and a new hot bar to fill). I am still a noob on the MMO side of ESO, but my question comes from I play the single player game.

In Skyrim for example, most of the time, I carry the following and use 'em all when the need arises.

One handed Sword for spells and arrows

Shield for spells and arrows

Two Handed Sword for Tanking above ground

Bow or a Crossbow for long range Sniper kills in dungeons

Dragger for the max sneak damage in dungeons

On my hot keys I have these spells:

Fireball

Heal Spell of some type

I change to any weapon type or hot key spell on the fly in any given battle.

That is my play style in a nut shell

What is the best way to have the same style in ESO with one weapon Swap (and one extra hot bar)?

Do you think like 20 or 25, one get yet another weapon swap and hot bar?

You won't get a third. You can set up your first hot bar and weapons to be the one hand sword like you state above.

Then you can set up the second bar to be any of the other set ups you like, it really depends on the situations of the moment which set up you'll be using.

I am planing on having one set up being pure damage, offensive abilities on the hot bar with a destruction staff, then the second set up to be more utility based, so to have some more survivability and control spells.

Although one question rises for me. We know we can swap weapons out, but does this include armour too?

I don't think so, unless it is out of combat

I thought as much, since you can weapon swap in combat then, looks like theres no armour changing mid combat.