wait, what? highest bidder? these things are auctioned off?
Answering this question first: No there is no auction. What was being referred to was choosing who to sell back to.
To clarify this better, when you purchase seeds you can only use them on mobs in the region (AKA the town you go to if you SOE) where you bought the seeds. Once you have harvested the fruit of those seeds, you can sell the mature fruit to ANY manor which is buying those fruits. Thus you can buy seeds for one area if the mobs are better for you or because only that manor is selling those fruits, but you are under no obligation to resell the fruit to the Lord of the manor you bought the seeds from. You are free to sell to any manor which 'offers' (buys) those fruits back for the best value or reward type that is available if you so wish it. There is a slight 'handling' fee if the manor you are selling to is not the one you are standing in front of however. (AKA you can sell fruit to the Dion manor even if you are standing in front of the manor agent in Rune.)
Back to your original questions now:
1)Current Seeds. Residual is the amount of seeds currently left for sale, Sales is the total amount of seeds that were made available for purchase that day and Sales price is simply the cost per seed the manor will sell to you at.
2)Current Crops. The manor can only buyback a set number of fruit per day. The maximum buyback is labeled "Buy", if some but not all fruits are 'bought back' then "Remaining" is how many more the manor is able to purchase that day. Buy price is the 'value' the manor is redeeming your fruit at. Reward (I or II) is simply the material that you receive instead of adena, the amount being determined by 'value' * the number of crops you are turning in. Thus, if you have 10 fruits you are selling back and the buyback is 200a, you will recieve (200 * 10) 2,000a 'worth' of the material as indicated by the reward type. If this was for example the Dion Manor and Thorn Cobols, you would receive (2,000 / 100) 20 Stems (Type 1 Reward) OR (2,000 / 2,000) 1 Metallic Thread in return. (Type 2 reward.) To get the value of the material to calculate your potential rewards, simply take one to an NPC and find out how much they will buy it for. The 'value' of the material will be twice this amount.
(A reward type of 0 simply indicates that fruit is not being purchased and no reward was set.)
For optimal seeding, the mobs should be white or green to you, and your level should be at least the minimum for the seed you are using. (Each one will give you it's level range in it's description.) Most seeds will work fairly well on mobs up through 10 levels over their stated level although there will be more failures to sow. There is no penalty to harvesting green mobs or above, but purple and blue mobs have strong penalties. You can sow yellows and above, but the failure rate does once again rise. Each seed has it's own basic rate for success, which means not all seeds will be 100% return on 1x HP mobs even within their 'ideal' level ranges. Some will be less than 100% and others well above it. Seeding multi-hp mobs (if you can kill them easily) offers the most return per seed and added success rates. And some seeds work a bit better above their stated level than their success rate within would indicate.
Basically however, if a seed says that it works best on mobs from level 5 to 15, your character should be *at least* the minimum level (5) before is uses the seed. Using a lower level char with a higher level seeds gives you more failures at sowing. Conversely however, using that same 5-15 seed on mobs higher is often more productive than when used within 5-15. (Each seed is different however, so try before going all out.) In general however, Seed level against your level should be the guide for sowing, and only mob level considered for harvesting.