Biking decisions - looking for a beginning adult bike

So my husband loves to bike. Seeing him do it and hearing how much fun he has makes me want to try biking. I have visions of our family biking around. This means I need a bike. The problem: I never biked much as a child or youth and I'm terrified of falling over. (My balance isn't great.) So I'm trying to find a bike that I can get on and off easily and put both feet on the ground. I want to use it to ride around with my husband and kids and potentially pull a bike trailer with the younger ones in it.

Use the mountain bike I have
cost: $35
pros:

• cheap, I already own it
• It's a decent bike
  

cons:

• not the right size
• bad memories
• saddle hurts
  

explanation:
I got this bike at a yard sale a few years ago for $35. It needs a different saddle and the frame is a little too big for me. I've fallen over trying to get off this bike, so I'm a little worried about riding it again.

Get a cheap beach cruiser / hybrid
cost: $75 - 250
pros:

• can get a step through frame to make getting on and off easier
• If I don't end up liking riding a bike, I'm not out a lot of money
  

cons:

• probably will be steel frame so heavy and rusts easily
• you get what you pay for
• A lot of beach cruisers are single speed
  

explanation:
A hybrid or a beach cruiser seem like what I am looking for, the step through would make it easy for me to get off without falling over. The cheaper bikes (like at wal-mart) tend to be heavier because they are made of steel.


Get a nicer beach cruiser / hybrid
cost: $350 - 600
pros:

• Step through makes it easy to get on and off
• some have forward pedals that let me put my feet down on the ground without having to have the seat to low.
  

cons:

• expensive, especially since I don't know if I'll use the bike
  

Gears
Single
cost: $75 - 200 (depends)
pros:

• very simple mechanically. if I got one from wal-mart there isn't much that could go wrong
  

cons:

• towing is harder without multiple gears
  

three
cost: $100- 200
pros:

• more gear choices
• many have automatic shifters so that the chances of the chain coming off the derailers is slim. Also, I wouldn't have to be moving to change gears
  

cons:

• more speeds make towing easier
  

seven
(same as 3 except the shifters aren't internal)

21
cost: $175 - $600
pros:

• best for towing
• more complicated for me because gears make no sense

cons:

• chance of chain slipping or jumping

explanation:

breaks
coaster

• stops, but not great for towing

hand breaks

• stops the bike

Where to get the bike:
walmart

• cheap
• bikes assembled for you
• easy returns
• quality issues
  

on-line

• better "bang for buck"
• have to assemble it yourself
• returns would be a pain
  

bike store

• usually better customer service
• knowledgeable customer service
• can help you choose
• more expensive prices (bikes start around $350)
  

classifieds

• can get a good deal
• have to know enough about bikes to tell if the bike is in good shape
• no returns
  

Summary
I think what I want is an inexpensive 3 speed bike with hand breaks and step through aluminum frame. I'll probably get it online or from wallmart. My husband is good at bikes and can help me assemble a bike. I want a bike that will need less twiddling, so a three speed would probably be a good match. Since I don't know what I like in bikes, an inexpensive one would let me discover everything I hated about it so when I bought a new, I would know what to look for. Also, I could ride my husband's old mountain bike if I needed more gears.

(update 9/22/10)
I ended up getting a 21 speed Forge Athena from Target.  It was a pain to get set up, but it seems to be a good bike.