I have included a link to the 72 cell version of the setup I have below.
They are 1 inch square and have a plastic greenhouse cover.
I don't plan on growing a lot of plants. Just enough herbs for two people.
In addition to the Bell Peppers I also have seeds for Thyme, Rosemary, Sage, Oregano, Basil, Cilantro, and Parsley.
I have no light or heating pad but I was told since I live in Texas I can take the greenhouse kit outside into the sun in the day and would not need additional light.
Would any of these benefit from multiple seeds in each of the 1" cells?
Would any of these seeds NOT benefit from being grown this way or would be better if sown directly?

http://www.planterspride.ca/en/product_details.php?cat_id=2&id=11

Cilantro is not one that should be started in cells. Its better to directly plant outdoors, as it does not transplant well. A single seed of cilantro in a 1 inch cell will not be worth the bother, as I mentioned in another recent post. If you leave these outside in bright sun. the temps inside the dome can reach well above 130 degrees, which can cook a seedling. Allow a bit of ventilation while the cover is on. Once the greens touch the cover, remove it. New seedlings need warm temps at all times while they germinate. Direct sun can also injure some of them, until they get their first set of true leaves. If growing under plant lights liek florescent types, the lights must be left on at least 18 hours per day to be effective

Cilantro "seeds" are actually a nutlet. Each "seed" will produce more than one plant.
I have absolutely no trouble transplanting Cilantro-either from a small cell (288 per tray) with 3 or 4 "seeds" per cell, from a larger cell (32 per tray) into the garden or large planter, or those that are sown in a row (shallow flat with no compartments) and pulled apart at the first true leaf stage and potted, in clumps of 4 or 5 plants, into a small pot. Cilantro is short lived though-it only produces foliage for 6 to 8 weeks before it flowers and begins seed production (coriander).
We sow or used to sow all our herbs in rows in open flats then transplant in clumps when the seedlings have 1 or 2 sets of true leaves. I sow peppers and tomatoes the same way but after being separated are planted one per pot. I wouldn't worry too much about spacing seedlings-as long as you have good air circulation they should do just fine. If you are worried they might be too crowded you can always thin them like you said by removing the weakest one. I now do basil, cilantro and parsley in small cells (392 per tray-5 to 6 seeds per cell) just to speed up the transplanting process and reduce shock-the plants grow quicker too.

Coriander is actually a fruit. Here, it grows sideways and twisted and has never matured properly for me. Starting a pot with a bunch of coriander makes harvesing the thin stems and leaves much easier. Coriander doesn't like a lot of hot sun either. Same transplant problems with dill. My tomatoes and peppers are started with one plant per 2 inch square pot. They usually reach about a foot to two feet tall by planting time, and are very early to flower.

In my opinion planting more than one seed in a cell is a waste of seed unless you have very little space available and must be sure every cell produces. I used to use cells but now I just use shoebox sized plastic containers with clear plastic lids filled with planting mix to a depth of two or three inches. For tomato seeds I space them about an inch to an inch and a half apart. I usuallly only plant a third to a half a pack of any one variety and save the rest of the seed for the next year, so I don't want to waste seed. After transplanting I recycle any planting mix left in the container for the next type of seed I am starting, so I don't waste any planting mix either.

Coriander likes being crowded, so its easy to grow a pot full of them for a single meals seasoning. I wouldn't do that with vegetable seeds though

Should planter cube be removed before planting Or will it rot away?

I am also new to growing herbs and what I had trouble with was deciding how many seeds to plant. I don't want cilantro anywhere near my garden so that one is not in question, but is there something that tells you that you need one plant (maybe Rosemary) and of other things you need multiple plants, etc. Do you sometimes plant a 'hunk of seedlings' rather than one plant. I have a lot of things started, multiples in a cup, but I don't know which ones to separate and which ones to plant as a 'group'.

soonergrandmom - it would be useful to know which herbs you have sown and then we can give you pointers for the specific varieties. Also some idea of your herb usage would help. For example, do you regularly use herbs by the handful or only as an occasional garnish?

This is a great forum for information. Also just typing in a question on the web will also take you to a few sites that provide added instructions so I enjoy looking both here and other locations on the web;

http://www.gardeners.com/How-to-Start-Seeds/5062,default,pg.html

http://www.robsplants.com/seed/starting.php

These are 2 just by typing seed starter and follow a few links. So like all things I enjoy I like to go site seeing also. Enjoy and have fun in your new adventure

I am new to starting seeds. How big do the plants need to be before transplanting. Any advise will be great.

Safyre--sometimes it is better to start a new thread rather than adding onto an old one.

As for your question, it really would help to know what plants you're talking about. (As to the OP where how many seeds really depend on the plant). Are you talking transplanting into pots indoors, or into a garden. Since Houzz got rid of zone info, where are you at? I'm in Denver, so starting seeds now would mean I can't transplant out until April/May at the general earliest (my veg garden is just in plans right now for seed starting soon). But I have lots of pots indoors for the winter. All are different--I have some newly sprouted chives that I seeded directly into their pots. But I won't start my basil for another month or so, because it shouldn't go out until end of May due to our night temps here.

Here in the Houston area they are already starting to bolt. I have harvested most of nine and froze them to be used anything within the next few months.