Does gilding reduce or increase the cost of the hero

The regilding is immediate. No fight needed.

You pay your two hero souls for the regilding, then you immediately get the screen like you just gor a new gilding and you have to click to open a chest to discover your new gilded hero.

When you ascend, you'll receive 1 hero soul per 2000 hero levels. (unless changed) Basically if you have a total of 5310, you'd get 2 hero souls.

Before you'd get cooldown reductions, damage, more gold and so on. But now I believe that you only get a % of damage. (you can read if you hover over the hero souls text) If I'm correct, it's 10% extra DPS per hero soul that you have.

I think I did my first ascension around level 100, but like I said, you had more/better extra stuff by then.

I'd say do an ascension whenever you feel that you are ready, then try to get as far as you can, without spending ages on each level, then repeat.

It's hard to say when the best level for ascension is but yer, I lost my savefile and I got pretty damn far. :3

Best of luck to you.