can I replace a gpsmap60csx and SPOT with a garmin inreach explorer+?
Probably. The InReach GPS functionality isn't quite what the 60Csx would be, but it will do the basics. Check the specs about number of routes, waypoints, trackpoints, display resolution, memory, etc. to be sure it will suit your needs. But overall, that's the idea behind the InReach Explorer+ - combined satellite tracking and handheld GPS.
inreach uses Iridium vs regular GPS satellites which supposedly is better under cover?
My buddy with a SPOT device borrowed my InReach and claimed this was true, but that's as close as I have to first hand knowledge. InReach makes this claim quite broadly, so it is probably true. Maybe there are others who have used both devices who can be more definitive?
regular gps's probably have better base maps?
AFAIK, all Garmin basemaps work with the InReach Explorer+. Plus, if you use the smartphone app (Earthmate), you can download additional basemaps at no charge.
is subscription cost for inreach cheaper than SPOT? (just need GPS to follow a gpx track, transmit to Trackleaders and ability to send and receive emergency texts when out of cell service range)
Yes, over the course of a year, the subscription plans (at least in Canada) are cheaper. You can use the device for a minimum of one month, and then put the subscription in suspension for $2.95 a month, or deactivate and reactivate for about $30. So as long as you use it for a couple months, at reasonable rates, the annual costs are very low.
And of course, the InReach provides two-way messaging, which SPOT doesn't do - that's the deal cincher.