1. Using the adobe media encoder (starting with .avi) the F4v file was 3000 kb and the flv was 1800 kb. Why such a great difference and is there any reason I need the f4v if I'm just displaying the video with no controls?
2. Both frame rate and bitrate seem to affect the final file size. If I encode at 1500 kbps an.flv that will be progressive download, does that mean the end user must have internet download speed of 1.5 Mbps or better to have this video start immediately and play smoothly?
flv will work fine for you. Playing with data rates and frame sizes will let you reach a trade-off for image size, file size and quality.
With the bitrate, yes, if you set a high bitrate your user will need appropriate bandwidth to view it without pauses while the video "buffers". And of course the user may be doing other stuff with their bandwidth while viewing - running on a vpn, downloading in background, whatever.
You have to judge whether the trade-off of bad performance for users on slower connections (including some users with shared network access and limited outside bandwidth in offices) is worth the better quality for luckier users that a higher bitrate should bring.