My question is can I have a greenhouse that produces fresh produce all year.

It is defiantly possible to have a greenhouse that produces all year, although you may decide it is more economical to freeze or buy produce in deep winter. Mid Dec.-Feb (in the northern hemisphere) is going to be the most difficult for vegetable production due to low light and cold temps. However with enough supplemental light and heat anything is possible

Next to which side of a house should we build a greenhouse?

The choice of which side of a building to put an attached greenhouse depends on how much light you want and need. The north is usually a bad choice, unless you are growing very low light plants. For hobby greenhouses the west or the east, with the west being bit better (because it gets the afternoon sun) offer enough light to grow most plants. The south provides the most light but also the most heat, this may be what you want if you are building in Alaska. Of course all this advise is based on building a greenhouse in the northern hemisphere :-).

I want to grow flowers and houseplants in my greenhouse. What is the temperature the greenhouse should stay at?

The temperature you need to keep a greenhouse is entirely dependant on the type of plants you are growing. Some flowers such as roses can take high temperatures up to the low 90's, if they are well watered. Others like tulips and ferns need a cooler, shadier climate to thrive, say no higher than the mid to upper 70's. If you live in a warmer climate you may have a hard time with the plants that need relatively cool temperatures like the tulips.
One other thing to keep in mind, the combination of a dry plant and a high temperature equals a dead plant. If your plants have to survive a couple days of high temps make sure they are well watered.

We live in the Wet Mountains of Colorado and have some concerns about the type and design of a hobby greenhouse. Two factors are altitude and seasonal winds from time to time, gusts as high as 60mph, with sustained winds of 25-35mph. Our snowfall can be from inches to two or more feet in a single storm, so that load factor must be taken into account. Our question would be what is the best design (free-standing) and what type of materials do we need to consider with the above factors in mind?

I would suggest a quonset style greenhouse with an gothic arch that comes down to the ground (no straight sidewalls) You will want to keep this greenhouse away from other buildings so the snow can slide off to the ground (the snow doesn't let a lot of light in ;-) As for glazing materials, I would suggest either polycarbonate, or polyethylene with the preference being polycarbonate. The polyethylene is cheaper and will most likely last 3-4 years in your location. It does tend to flap in the wind more. Polycarbonate is very tough and will take the wind better plus it just looks better. Most polycarbonate comes with a 10 year warrantee against yellowing, and would be valid for your location. When you size heaters for your greenhouse, make sure that you derate them for your altitude. The combustion just isn't as efficient in a gas heater at 7,000 ft.