I would definitely try it. That's how I got started in AG, I figured if I halved the recipe, I could still use my 5 gallon pot and brew inside, although I did make a Igloo cooler mash tun. It turned into the best two beers I have made so far, even though I only got about 50% efficiency. I've been brewing AG since, and trying it in small batches inspired me to get the equipment needed since they turned out so good. Like the previous post, I wouldn't worry about a secondary yet. I was told early on that it was very beneficial to use a secondary, so I did for every batch, and I think the result I got was maybe a tad bit clearer beer, but was oxidized when it didn't have to be. One nice thing about 2.5 gallon batches is you can experiment a lot and brew a lot more, without as much of a backlog of beer that you need to drink.