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Yes, you can go ahead and do so now but it may interfere with the future flowering of those that haven't yet bloomed for this season. They will, however, bloom again next year.

Typically bulbs are not sold by the gallon. But if you found a site that does sell them this way, I would recommend contacting them and asking. Even among the same species, bulb size can vary greatly depending on the quality of the bulb, age of the bulb and the variety.

Here are some answers for you: https://www.gardeningknowhow.com/ornamental/bulbs/bgen/preparing-bulbs-for-winter-how-to-store-bulbs-for-winter.htm

This article answers your questions: https://www.gardeningknowhow.com/ornamental/bulbs/bgen/is-it-too-late-to-plant-bulbs-when-to-plant-bulbs.htm

Yes, this can in theory work, but with Mother Nature there is no guarantees. Inclement weather or pests can destroy bulbs. I always advise people who are growing things for a specific event to make sure that you have a backup plan in the event it does not work.

You may find the section on hardy bulbs in this article helpful:
https://www.gardeningknowhow.com/ornamental/bulbs/bgen/storing-bulbs-in-south.htm

I'm afraid we'll have to narrow your question down a bit. What kind of flowers are you wishing to grow is first? You need to decide on variety first, because some bulbs are planted in the fall, some in the summer, some in the spring. Once you decide what kind of plant you want, you need to find out if miniature varieties are available. Then you can google "where to buy [whatever kind of plant you want] in northern VA [or your metropolitan area]" That will give you both online and local sources.