There were supplementary harnesses made by a couple of inmates here but they are no longer available.
The so-called S4 spider was the subject of a recall for 2006-09. You can check the VIN with Yamaha to see if it was done on your bike. This is the one most likely to cause an issue although there is one other ("S6", I believe) that has had some issues.
Read this about the recall
https://static.nhtsa.gov/odi/rcl/2011/RCRIT-11V338-2345.pdf
Read the following thread that discusses another non="spider" ground issue. Thread also has a map of the electrical grounds.
https://www.fjrforum.com/threads/itsy-bitsy-spider.158418/
These aren't that difficult to fix if you run into a problem. A matter of diagnosing, finding it and modest soldering skills.
I didn't think that '08 came with heated grips except in the AE (auto clutch) version, but I may be mistaken (my '07 didn't but my 2011 did). They could be added with an OEM or aftermarket kit. The foam grips may be Grip Puppies foam covers with the regular grips underneath.
Everyone has a different tolerance level when it comes to seats. In the last 13 years, I have put close to 300,000 miles on two different Gen II FJRs with the stock seat. Some people whine if they had to ride across town without their Russell Daylong.