Alot will depend on what you consider a "good yield", as well as the strain you are growing. There are many others here who can provide a better answer to your questions but im sure they will want to know these things.
To produce the optimum yeild out of 1 plant you need to find the ballance of space, time, light, and nutrients. It takes several grows of one strain done several ways to find the optimum growth for optimum yeild.
It also will matter as to how much vertical space and lighted area you have, and the strain. I have seen some plants that were grown 6' tall but only about 2' in diameter. They had tremendous yeild. Others I have seen grown only about 3-4' high but very bushy and about 3-3.5' in diameter. My partner and I try for this short and bushy type as that seems to yeild very well.
I would recommend as a rule of thumb to allow them to veg until your space is a little less than half full of plants. The vegging time really depends on how you grow them (any type of training) and whether they are from seed or clone. Growing from seed will require more time so that they can get to maturity before flowering. Clones can be flowered as soon as they have a good root system(if you are height limited this is the way to go).
For any given space, you can either set many single stalk, small clones close together to form a sea of green. Or you can set fewer plants in a more spread out position and do a little training to keep them low. Or you can set a minimum of plants with a lot of space between them and train them to become bushes that will mostly take up the growing space.
If all of the conditions for the given growing space are very good from start to harvest you should get about the same amount of yeild out of any of the above examples. It really comes down to what setup works best for you.
If you would like some suggestions, give us all of the details of your grow and you will get all kinds of suggestions. If you would like individual help you can pm me or most of us for individual suggestions
My grow is a 4x4x8 grow with a 600w hps. I have clones, fox farm soil, fox farm trio mutes. Ph always balanced I have 3 gallon pots. Panda film surrounds the grow. When I feed should I have a set temp on the water? Fan to circulate air
You will need air movement provided by a fan inside the room and another for recirculation (to bring fresh air in and exhaust the old air). Watering temp isn't too critical, most just go with room temp water. . .
Well, as a starting point I would only veg them until they were about 15" tall. At that size you should be able to average 2oz/plant if you can avoid any catastrophes. You can adjust from there if they overgrow or don't fully fill your room.
No reason at all that you cannot expect 3-4 oz plants, however I do not see 8 4 oz plants in a 4 x 4 space--a 4 oz plants is a good sized plant.
Since these are clones, how large did the plants these came from get? That is a big part of deciding when to flip the lights--knowing how large your plants are going to get. Indica dominant plants that do not stretch much can be allowed to veg longer. Sativa dominant that stretch a lot have to be put into flowering smaller. Remember that more plants do not necessarily mean more bud (IME 8 2 oz plants in 75 days vs 4 4 oz plants in 100 days is not a valid comparison).
I have a 3 x 6.5 sq ft space and I never put more than 8 in there.
While I don't disagree with Kiks, I agree more with Goddess. If you put all 8 plants in a 4x4 space and veg them to 15", you will have nearly a sea of green (depending on the strain and phenotype of the plants) If these plants tend to grow straight up, narrow, and lanky then you could do 8 if you flip them at 10-12"(this is a bit of guesstimation for plant type) and allow them to grow straight up. They should stay short enough for the light to get to penetrate down the sides of the plants.
If the plants tend to be more bushy then having 8 is going to give you a solid top canopy which is the sea of green, which in my experience doesn't produce as much per plant and less per sqft(again my recent experience). If bushy is the case then I would only put 4 plants in and veg them a little longer, spread them out some, and do some branch bending n tieing to open the plants up. My recent experience with this method makes a open forest of green rather than a sea of green. The difference being that the open forest allows more light penetration which gives multiple, taller, more filled in buds on each plant.
Given that you are in 3gal soil buckets I would go with the fewer number and the "forest" training. This may also make it a bit easier to water and feed them. 4 prefferably, 6 plants at most, and keep the other 2 as back up mothers for catastrophy protection.
Best way to increase your yield mrs lady is to study up on topping (which will make your plant extra bushy) and study lower stress training which will give you multiple tops. Truthly I recommend a SCROG because when you SCROG when flower time comes all your budsites are pretty much on a level plain receiving almost the same amount as light. I will never again just grow a plant straight up. LST WILL GIVE YOU GREAT RESULTS.
I AM NOT A EXPERT. MY TECHNIQUES ARE NOT ALWAYS TO STANDARD. I AM A ROUGUE GROWER. GOOD LUCK IN YOUR ADVENTURES.