Hey Pam - There are lots of experienced long distance riders on this site. I'll add a couple of comments that you might consider -
1 I realize they do not provide much protection but in temps above 90 degrees I usually just wear my favorite loose fitting jeans. Both you and your passenger could stand up on the pegs on occasion to air out (Just NOT at the same time).
2 Seat cushions are a matter of personal preference but I usually just buy a USED sheep skin seat cover off Ebay (Mercedes/Porsche - owners hate a worn place on their side bolster and often sell a $150 full size genuine sheep skin for $20)- cut out the worn portion leaving a generous rectangular shape. Take the GW seat off and sew the slack edges of the sheep skin in a criss-cross pattern on the underside using heavy nylon fishing line. I've never had one come loose and they feel great to me. You can also buy a very inexpensive used set of Seat Beads to cut down as well. They are surprisingly comfortable on a long haul.
To avoid another unexpected dump over in a parking lot - I always modify the kick-stand foot a bit so it doesn't sink into any soft ground. The added "Duck-Foot" (?) is simply two pieces of heavy aluminum bolted together to increase the diameter of the bottom of the kick-stand base.
3 On many early 1500 GW's their cruise control option never did work well for me - so I'd fall back to using both a Mechanical Locking style device and a Wrist-Rest device. The Mechanical Locking device simply pinches or squeezes the right throttle control to hold it in position when you push down on the locking lever. It can be quickly released by flicking the lever up or just over ride the friction lock by simply rotating the throttle. Mine is pictured at the far end of my throttle control.
The Wrist-Rest is simply a "C" shaped piece of plastic that is attached to the very end of your throttle control. I use this as my cruise control most of the time. They are around $10 but I made one from a piece of PVC pipe (slightly larger than the diameter of throttle) with about 1/2 cut away. A little glue and a couple of small wood screws drilled into the end ring of the throttle control permanently attaches it. Install the Wrist-Rest with it's extended arm approximately level with the ground. This will allow you to completely release your right hand grip and hold the bikes speed steady by resting your palm/wrist at a surprisingly comfortable mile eating position.
I also added a pair of new cushioned foam sleeves over the original handle bar grips for extra padding. The dual layers of foam will provide nice oversized cushioned grips which really feels great.
4 A power phone, gps, gizmo charger can be added very easily by tying into any +12 source. One Red wire with a fuse is attached to battery voltage and one Black wire to ground. Any necessary internal voltage conversion needed is handled inside the coupler you buy.
5 Adding some LED lights is also pretty straight forward. I like the (Dual Mode) LED Running/Flashing Lights for safety. Mode 1= Both LED Lights are On Steady For general Traffic Intersection Attention or To Light the Way At Dusk. Mode 2 = Both LED Lights Flash Alternately for "Look Out Ethel sitting at a Stop Sign - Don't Run Over Me". The Dual Mode LED lights will require a fused three position toggle switch On/Off/On.
6 It may take a few miles before a new passenger feels comfortable on the back of a bike. You might make a few shorter trial runs first. Just give yourself lots of cushion in traffic and make sure to take it easy when accelerating and braking. When my wife accompanied me on my 1500 I would communicate A LOT to make sure she knew everything was OK. As far as banking into a curve - I had my wife always just stay relaxed and sit up straight throughout. With you handling the tipping angle - it will give both you and your passenger a reliable, smooth controlled and consistent amount of lean every time. Like others have already mentioned, if your passenger doesn't feel comfortable at this early stage of ridding - perhaps a later trip would be best for them.
Ride Safe - Michael