It seems like a very good deal, depending of course on what kind of head is on it and what quality the lenses are.

The D3 is the autofocus "D2" and adds some convenience to the darkroom. I'm assuming that this enlarger has the condenser head. Is it the variable condenser type? This would add to the value of the enlarger as well as making format changes much easier.

At some point you might want to get a colour head or a cold head. That will reduce your print spotting and should offer a more even light. If you do get the colour head it will also replace polycontrast filters, which never hurts.

As for printing 35 mm and larger negatives: I used a D2-V at university for 35 mm printing with a 50 mm lens and had no problems with it at all. My current enlarger is a D-6 with a colour head and a three lens turret. I've found it next to impossible to use a 50 mm lens wit this setup. The bellows has to be compressed as far as it will go and I can't think that that can be good for the bellows. Subsequently I use an 80 mm lens for printing 35 mm negs. The images are sharp, I have more reasonable exposure times (the colour head is VERY bright) and I have more room for my hands in order to burn and dodge. The seller can tell you if they have had any problems with this.

One of the great things about the Omega d series enlargers is that they are as common as dirt. For every other 4X5 enlarger you'll find 10 Omegas. So you'll find lots of used accessories out there. Things like negative carriers and cold heads for example. And if some third party is making an accessory for a 4X5 enlarger, making it compatibile with an Omega D is where they'll start.