Yes step one with multiple gremlins on this car is ALWAYS the battery...

1. Is the battery the correct specs for the car? If not, replace it with a quality battery of the correct specifications.
1. Is the battery 5+ years old? If yes, replace it with quality battery of the correct specifications.
2. Charge the battery fully (disconnected from car), let it sit overnight, then test it:
a) A voltmeter is a good start, you want at least 12.3V and even that's not great 12.4V would be better. If not, replace it with quality battery of the correct specifications. A low voltage indicates the battery is a bad. But a good resting voltage does NOT guarantee the battery is good...
b) If resting voltage is good, then load test the battery, either with a cheap home tester or just take it to the parts store, they'll do it for free.

If all that checks out, make sure all of the ground straps and wires got replaced and the connections are clean and tight. Easy to miss those when putting all the parts back on.

As OldKarz said, make sure all the harness connectors are snugged up tight.