Hit an electrical wall

I need help with Electrical.
1999 Toyota Camry le 2.2lt 4c

All factors leading up to backdown
*Aftermarket boss stereo with back up camera wired wrong by x. (I've unhooked and took out since break down of car) Hit a dip going a lil 2 fast, when stepped on brake car would loss power including stereo. (3 weeks b4 breakdown)
Day of break down: driving from Las Vegas to Cali. Checked all fluids and got gas
Right pass weight station in Cali (pass border) driving up incline I shifted from D to 1 to 2 back up to D all in 5 sec time. - caused speed sensor to fail. (New speed sensor put in)
*Secure bar for battery loss. Grounded out positive side of battery cable. Both have been replaced. This I believed to of fried the starter, starter relay (under hood) and fuse (driver compartment). All houses lost power as well.

Put in new starter, starter fuse and relay.
New battery cables
Spark plugs and valve cover gaskets.
Also my 10A HeadLh fuse and socket was blown.
OBD2 reader comes back with no codes but when I use the other locations I get back code 31 which was the speed sensor. I also cut out the after market alarm.
How can I get power to terminals safely? How would I wire them? Also how would I know if my ecu was messed up because of this grounding out? Help me please I've hit a wall