To answer your questions in order:

- The Cold Steel games comprise one arc (Erebonia arc) in the overall Trails series. They are not completely separate from the Sky games (Liberl arc) - the events of Cold Steel continue from Sky, and there are cameos and references to the earlier games. Most hardcore fans will tell you to play Sky first before touching Cold Steel. However, there is really nothing stopping you from starting the series with Cold Steel. Sure you'll miss some references, or have some events from the earlier games spoiled, but Cold Steel can be enjoyed in its own right.
Also, the different games have their own charms - if you find yourself drawn to Cold Steel over Sky, why not go with the one that interests you the most? Just know what you're getting yourself into.

- Correct, on PC there is no deluxe edition, you'll have to buy the DLC separately.

- Correct, previously English audio was the only option available in the official release. You are right that there was an unofficial patch before - but the official update adds the exact same audio files (WAV format), so there's no need for the old patch anymore.

- It depends on what your criteria for "worthiness" of pricing is. If you're just looking for a good deal, the current discounts (-40% for the first game, -30% for the second) are the best they've been yet. Judging by historical prices, it looks like the discount will be the same for 2+ sales in a row before another drop happens. So it's likely the price will not be discounted further during the Christmas sale, but maybe the next one or one after.

- In terms of romance, this thread may be of interest to you. tl;dr - yes there is romance, but it's very light

Hope this helps!