IANAA and you'd be best to ask for professional advice off-forum, but...

1. You say the apartment block is on the accounts at 580k yet the accounts show the block + land at 640K. And then you say you're selling the apartment block with land on it's own. A bit more information is needed here to get the figures correct. Does the 640k include additional land? Is the 580K the original purchase price? Has depreciation been deducted and claimed in the tax returns in previous years?

2. Hard to determine without looking at previous years' accounts and without knowing more about the swiss tax system.

3 and 4. That great source of information, Wikipedia, states: "There is no capital gains tax in Switzerland for residents. Corporate capital gains are taxed as ordinary income. Capital gains tax is charged to individuals on the sale property if sold within 10 years of purchase."

Considering the sum involved, it would appear wise to seek qualified professional Swiss advice, especially if there is a possibility of the real estate transaction can be transferred to the individual and the ownership is more than 10 years.