Modesto is arid, dirty and mostly farms and migrants. It is filled with the gangs you're so very worried about. But!!! most of the crimes perpetrated are on each other. Not mid-westerners
. It's okay if you're traveling alone. Not a place I would bring a family.
On the other hand you're juxtaposed right there against the southern range of the Sierras.
Yosemite is a hop, skin, and a jump away and is magnificent!
San Jose and San Fran are a little farther to your west and you will never run out of things to do over in the Bay Area.
Lake Tahoe... Sacramento, Redding, Mt. Shasta. Modesto isn't the worst place you could be. It's not Detroit after all...
How long is your commitment? 1-year 2-years? Make sure you identify the parameters of your bonus (in writing) in case you want to relocate again when it is over.
You definitely want to rent. Don't get into any mortgage out there when you don't know if you're wanting to be permanently placed there. Plenty of places to rent. You can also commute from the surrounding communities pretty easily as well.
Pay is competitive enough if you throw in your bonus. Bay area wages are a little higher. You never know unless you try. If you're looking for changes in latitude and since they're covering your costs I say DO IT! You have nothing to lose.