NFTHarbor is a system where nft(s) can be traded on the Galachain (GC) network. Payments can be done on any network (ETH and Galachain at this time)
Buyers will be able to list their NFT(s) while potential buyers will be able to buy, make a bid or create an offer for items that are not yet listed.

No. Any NFT will still be in your possession until you manually put them in the escrow. This is only done when a deal has been made with the buyer and the fee has been paid.
Be sure though to keep your NFT(s) in your possession when a deal has been made. Otherwise you will loose a star which gives you a bad reputation (and punishments)

Everybody will receive at the start 3 stars. For each deal made, the seller and buyer need to perform some 'tasks' in order to deliver the item from A to B and perform the payments.
If you do not accomplish a task when its your turn, you will loose a star. This results in higher fees and in the end you will not be able to trade anymore.

The Fee to trade is 0.5% on Galachain (GC) and 1% on ETH chain. This will be higher in case you do not have 3 stars anymore.
For Swaps, its default 200 Gala. This can be divided between buyer and seller as well.

In the "Deals" section, you will be able to follow a deal. There are several steps that need to be performed:
The Seller needs to pay the fee (by sending the fee from Galaswap or Gala site to the GC address mentioned)
The Seller needs to send the NFT(s) to the escrow (by sending the fee from Galaswap or Gala site to the GC address mentioned)
The Buyer needs to pay the Seller. We do not keep any payments, so make sure its the correct amount
The System will transfer the NFT(s) to the buyer

A buyer has the possiblity to create an offer for items that are not yet listed. A potential seller can then come along and accept the offer, resulting in a deal.