Take a look at the plastic trough style planters. These can often be found at big box store garden centers for cheap (2-8 dollars). Sometimes they are even self watering containers. They should fit really well without breaking the bank. As for weight, water is the main factor. It's approx 8lbs per gallon. A plastic trough and dry potting mix probably don't weigh more than a pound or two, but wet can get heavy. I am thinking of a 6" wide by 6" deep by 30" long self watering container I have and when filled including the 1 gallon it holds in the reservoir I don't think it is more than 15 pounds or so. I think your 150lb limit per shelf would be fine.

Boy, I dunno; I'm sure anything, diluted enough, would work. I personally like to use a diluted fish/seaweed emulsion (well, I don't like the SMELL, but I like the product). It may just be in my head, but I like that it's organic and I feel like I have less of a chance of burning the seedlings since it's not made of chemicals. But that's just my uneducated opinion. Most things I don't fertilize too much anyway, since I can hardly keep up with potting up the seedlings that are growing like crazy already. So I mostly just use it on the slow-growing plants and the heavy feeders. I'd hesitate to use Miracle Grow, and find something geared especially for young seedlings or transplants instead. Under fertilizing is better than over fertilizing.

I've done tomatoes from seed a few times over the years. I tend to try to use local (the most local being my property) resources. Somewhat successful but far from optimal. Luckily in zone 8a I can plant seeds directly in the ground early April and get a load of 'maters but it doesn't replace being able to start from seed early. Spring in February :) This year I actually bought some ingredients :( for starting my seeds, peat and vermiculite. For about 2 gallons of mix I used 1 part peat, 1 part vermiculite and 2 parts homegrown worm castings. To that I added tight fists of green sand (3 fists), bone meal (2 fists) and blood meal (1 fist). I planted 1 tray(24) of Better Boys and 1 tray(24) of Marions. Germination started on the 7Th day. At 3 weeks, I fertilized each plant with a big pinch of the same part fert mix above. Today is week 5 and the best plants are about 6 inches. Constant temperatures are not optimal as the plants are outside except very cold nights. I had no germination on 4 Better Boys and 2 Marions. I lost 1 Marion (droop) at about an inch tall. The Marions are an inch shorter. So with this mix I got 41/48 or 87% to transplant height. Question (to myself at least): How will I effectively replace the peat and vermiculite with a local resource and get at least a 70% rate?

Desen I am not sure what you mean by hurting or damaging? - are you talking about taking off the leaves? If so, obviously you don't want to take all of them off. Taking off few should not be a problem. Leave them as they are, do not wet the leaves. Roots usually appear in short while, sometimes little plantlets first. There are some echeverias that do not want to grow from leaves, but most will if the leaves are healthy enough. Maybe you could post a photo of your succulent (or any if you have more than 1).