What's a good first saber? Easy. The one that calls to you from the listings. Every saber has it's pros and cons, and everyone is going to have slightly varying opinions of each hilt. It's a personal flavor, personal touch decision. I would recommend starting your search with an apprentice saber. They're a little less expensive and a little more simple in design. If you don't fall in love with one of them, search through the elite hilts until you find one that does call to you. Just one word of advice on easy to use/spin/duel with... avoid control boxes. Some sabers, like the reliant can actually be ordered without the box.
As for battery you have only two options.. a 6w warrior set up comes with AAA batteries. 12w warrior, and everything else comes with an 18650 rechargeable. Warriors (except for the bane) do not have in hilt recharge. Blade width is all 1in. And the infinity edge v4 is the only blade that SF sells.
As has been said, RGBA is only an option on hero tier sabers, they are the only sabers with a board high powered enough to run the color changing options on an LED. Now, wattage is slightly misleading as wattage =/= brightness. Lumens = brightness and wattage simply refers to the power draw of the die in total in the LED unit. However, the RGBA functions on a 4 die LED unit, lighting and mixing seperate die at once, by themselves or all together. This does result in less brightness, yes, but especially in a 26in blade that's not going to be detrimental to the brightness level. And all the settings and color changing is 100% customizable on the SD card and the on board color menu, you just need to set it up how you like it. You don't even need flash if you don't want it.
The blade retention screws are 8/32 set screws which if I remember correctly are 5/64 Allen wrench keys.
SF's sabers are 100% warrantied for full contact dueling (with the exception of crystal reveal sabers) so you do not need to worry about the internals with or without sound. I've had my sabers from SF go through hell and come out the other side humming happily. And if something does happen to go wrong, it's a simple RMA form away from being repaired by SF.
And as for colors, really that's all personal preference too. Get what you like. If you want something close to yellow, try amber (orange) or lime green (yellow green).
Any hilt customization concerns, keep in mind, need to be emailed directly to SF, and they can assist you with what they can do from there, if you wanted to get a custom finish on a saber or special requests on a hilt, etc.
(Ps- this took forever to write on a phone... fml)