We've just bought offplan and the whole think was fairly smooth sailing. We bought when the development was half finished, so about another 100 or so houses left to build. Roads still need to be finished, but that doesn't really cause an issue. No street signs, but lampposts are in. Roads won't get cleared due to snow... but I wouldn't expect them to.
We didn't have phone lines etc, but phone company get it all sorted in about 10 days. We had wiring to the house, but not connected to the property.
You may not be able to get a discount, I think something to do with they need the houses to sell at a specific price to guarantee the value of the other properties ... or something... you CAN get the fixture and fixings upgraded for free. Don't be scared to haggle. Ask for everything. You never know ;).
We got to pick all the fixtures and fittings, but the neighbour didn't as the developer needed the order in, but the plot wasn't reserved, so depending on what stage your property is at, you may not get to choose.
Freehold can be an issue if you want to remortgage or sell in 20/30 years. If you getting to the end of a leasehold, mortgage lenders won't lend. Some developers will give you the option to buy the freehold. My friend did this on her property and paid about 6k for a house values at 200k
We had a vague completion date until about 6 weeks before the house was due for completion then we were given a firm date. We got the keys the day we should have. Completion went through on the same day.