For how many years can I carryforward a capital gains loss? Are there any limitations regarding how much I can use in a given year? Any implications of new legislation?

A Capital Loss can be carried forward until it is used up, or until you die.

The Capital Loss Carryforward will first offset any Capital Gains for that year, then you can usually use an additional $3000 per year.

No, the tax reform has not changed anything in this regard.

But it must be claimed each year, even if it does not benefit you.  You cannot skip a year or the remaining less is forfeited.

Can I file an amended return for the year that I skipped to claim a capital loss and re-claim it?