I have a 1 1/2 hp series 1 built in 1972. This one looks to be in similar shape to mine. I did not view the videos in that I am out of town and have a very poor internet connection. BP's are good machines and are probably the cheapest of any to tool up.
If you're interested I would offer something in the neighborhood of $2,200.00 to $2,500.00. Both the DRO and power feed are ancient. The DRO likely will cost more to fix (if parts are even available) than it would to replace should it fail. The same is true of the power feed. There are several companies that sell parts, but by in large it's more cost effective to replace them with a more modern unit.
At this time I wouldn't worry about a VFD. The machine will run perfectly well on the static converter. I have been running mine on a Phase A Matic 3 hp converter for nearly 20 years with no problems. The speed change is easily done with the shift mechanism crank handle. Wait until you become more familiar with the machine and it's current capabilities before making changes. I think you'll find you'll want to spend the money on tooling rather than a fancier control system.
The downside is that you don't know much of the history behind the machine. Ask the current owner who was auctioning off the machine. Was it in a production shop, a repair shop, or possibly a local school? Some history would be helpful to determine how the machine has been treated over the last 30+ years. The serial number should be stamped near the front on top of the knee. Copy it down and go online to find the actual year it was built.
Here's a link to one of the many serial number charts available:
http://northeastprecision.com/calculators-bridgport.html
If it's in good condition, and the tooling you describe isn't all beat up I would say go for it at $2,500.00 or less.
As a side note mine came from a local high school. It didn't come with a DRO, power feed, or much tooling other than an original Bridgeport vise. I added a DRO later. Although it was several years ago the machine was in excellent condition, and I paid less than half what the owner is asking for this machine. So far I've spent less than $200.00 in repairs and upgrades other than the DRO.