[rabbit73]

Welcome to the forum, dtjones1987:

I have an Antenna's Direct DB8 antenna

Which DB8 do you have, the older one with both panels fixed facing in the same direction, or the newer DB8E with two panels that can be aimed in different directions? The ads claim that the DB8E can be used for two different directions, but it doesn't always work.

Where I live, there is already a Yagi style VHF antenna up there but it is not hooked up. I'd like to be able to use it to pick up Virtual channels 8 & 13.

That should work. Combine it with your DB8 with a UVSJ and then to a preamp.

The coax cable will have probably around 100 feet to travel (down from the antenna, will ground it, and then will have it come backup half way so it can go around the structure to where it will connect with the TVs.

That's a lot of coax. The signal loss for UHF is about 6 dB per 100 ft of RG6. And there is a voltage drop for the preamp power. Coax with a solid copper center conductor has less voltage drop than copper clad steel. You might need to move the grounding block so that the coax run is shorter, but the 10 gauge copper wire from the grounding block to the house electrical system ground is longer.

We have Dish Network currently and two TVs hooked up (it's one receiver that goes to two TVs.) I can't tell but I think there is splitter from the Dish before it gets into our house (unless they are hooked directly from the dish, but then I can just put them into a splitter) so we plan to hook the antenna into that.

You need to be a little more certain about your distribution system than that. Power for the preamp can't go through an ordinary splitter.

I wanted to see if there were any strong FM signals that would interfere with TV reception. I did an FMFOOL report based on an estimated location that puts you SW of the center of Dunkirk near a school. I don't see any problem that couldn't be handled by an FM trap, that many preamps have. See attachment 2.

A.) What kind of pre-amp or other equipment will I need considering the length of cable?

The preamps to consider are the Antennas Direct Juice, Channel Master 7778, and RCA TVPRAMP1R. The Juice has a low Noise Figure (good), is resistant to overload, has an LTE-4G filter to protect UHF TV from cellular interference, but doesn't have an FM trap so you should add one before the input if needed. The CM does has an FM trap; the switch default is IN. The RCA is OK but has some quality control problems. You could buy 3 for the price of one of the others. Sometimes the combined/separate switch doesn't make good contact with the VHF antenna in the separate position. The workaround is to use a UVSJ and the combined input.

B.) Since the antenna is multi-directional,

I wouldn't call the DB8 multidirectional; it's very directional. For best results, a directional antenna should be aimed at the transmitter.

if I point the DB8 toward Indianapolis, will it be possible for me to receive Dayton stations as well? I'm thinking I should be able to pick up, at least, the Fort Wayne stations as well from the back of the antenna, since I already do indoors.

Maybe, maybe not; you just have to try it in the roof location. I hope your tuners can add a channel after scan like my Sony, or you will need to rescan a lot.