It is possible that you are making a couple of incorrect assumptions. Let's check it out.
First, you said "I'm hoping this will allow me to experiment with different sounds over the lifetime of the keyboard rather than being locked in with the sounds that are normally built in to a digital piano."
Having built-in sounds will not restrict you. Most stage pianos can work with either internal sounds or with external sounds using MIDI. The external sounds can be a hardware synthesizer module or a soft synth running on a computer.
In that regard a keyboard with internal sounds is more flexible than a keyboard without sounds.
You said that "By moving the sound production out of the keyboard, I expect it would also be lighter and easier to transport (several smaller components instead of one large keyboard)."
The heavy part of the keyboard is the piano action. A true 88 key hammer action may weigh 40 -60 lbs. That is heavy.
The built-in sounds are just a circuit board that adds no weight. But if you carry a separate sound module or a laptop you are adding both weight and several cables to the mix.
In many cases you will be better off with a keyboard that has sounds in it. When you are in your studio, you can use a computer for the sounds but when you are transporting the keyboard you can use the internal sounds and save a lot of hassle.
As far as speakers are concerned, you also have the opportunity to bypass them in the studio and use them on the road. I have a keyboard which has speakers in it. They are fine for a small room and casual use. When I am playing in other venues I hook up external speakers as I do in my studio.
Decent speakers can be quite heavy. In the studio I use near field monitors. When I am gigging I use a heavy duty amp and speakers that in sum add about 100 lbs.
However, when I play at a friends house or informally, I use a keyboard with built-in speakers. At first I didn't want them but now I am glad that I have them.I can just pop the keyboard into the trunk and go. Much easier.
If you are not a very experienced pianist and don't require the nuances of a fully-weighted piano action, there have recently been a number of excellent keyboards that have excellent touch without a fully-weighted action. These keyboards weight around 20 lbs so are really portable. Casio and Yamaha make keyboards like this and they are worth a look. Check out the reviews in Electronic Musician and Keyboard magazines.
Wheat Williams suggests you need a "a three-pedal foot controller with half-pedal action." This is nice to have but you may be fine with a single damper pedal. That's a lot lighter and unless you use the other two pedals (I rarely do) it's just fine. You will find there are some nice ones that look and function like acoustic piano pedals and others that are just foot switches. I strongly recommend the former. Make certain that the pedal matches the keyboard you select. Yamaha uses different polarity from other keyboard manufacturers so look at the specs carefully. Some pedals have switchable polarity.
So think about how you will use the keyboard. If you never take it with you, you don't need internal sounds or integral speakers. But if you do, you many want to consider them. Keyboards and MIDI are flexible and you can use or ignore internal sounds and speakers as the situation dictates.