You have mostly UHF and some VHF channels broadcasting, so you'd be fine with an ANT-751 since you have Line Of Sight towers nearby. You *may* need an amp for distribution to the 4 TV's, but don't assume it will help regardless, as it can cause issues with strong signals like you have. I suggest first tuning the antenna while connected to just one TV. Once that's done, you can use a splitter to split it and see if you can still receive the channels w/o an amp. If the reception drops off, then you know you have reason to get an amp.
As for tuning, you'll want to aim the antenna north, adjusting it's direction as necessary, maybe a little NW or NE. When you scan for antenna channels on the TV, you probably can then check the signal strengths with the TV's diagnostic menu. Or you can just check and see if the flying pictures land on your screen without any break up.
The 100' run likely will require an amp. But....for the cost of an amp, 100' of direct burial RG-6, the effort of trenching, etc.....it might just be easier and about the same cost to pick up another 751 for the garage. That'd leave you with only a 3-way split required for the home, which may be fine without an amp. A little experimenting one afternoon will do the trick.
What I don't know is your tree/building situation. Anything in the way will block/degrade the signal, so the better view of clear horizon in the direction of the towers is best.
