Vaccinations are generally given at certain intervals over a period of early puppyhood. Every puppy will lose maternal antibodies (prenatal protection essentially) at a different time. By giving the vax's 3 times over a period of a couple of months they catch most of the puppies during an open window of reception and the puppy will then generate it's very own antibodies to the injected vax.
I have all small breed dogs, including 2 paps. I have all of our dogs complete the entire puppy series, and the first two rabies shots (usually given at 4-6 months and then one year later). After that I only do it on an "as needed" basis for classes or travel. Since lepto is not a problem in our area I do not ever let a vet give it to my dogs. We did have a serious problem with our first pap and lepto...I had to learn the hard way. We were doing foster work for the humane society and they provided free vax's for our own dogs, but the only vax they had included lepto. I didn't think it was a big deal at the time but quickly learned otherwise.
How much to give after the initial series of puppy shots and rabies is still up in the air for me. I'm waiting for some of the challenge studies to be completed before I make up my mind. And currently none of our dogs are in situations that require vaccinations like classes or shows. Their rabies are all current since they are only required every 3 years here. Preliminary rabies challenge info suggests that rabies could be protective for around 7 years after the first 2 shots. I haven't seen enough about the duration of the other vaccines to make up my mind.
Our vet believes that dogs are over vaccinated. So after the puppy series he offers the vaccines as separate shots, giving only one shot per year, no combos. So over a period of 3 years you end up getting everything in the combo. The purpose of fractioning out the combo shot is to reduce exposure to too many antigens all at once. It costs a bit more to do it that way (paying for 3 inidividual shots instead of 1 combo) but I think it's worth it. However, the vials for these vax's contain more than needed for one dog and the price to match. So the vet won't order it for just one client unless you are willing to pay for the entire vial $$$. Sometimes it pays to find a vet who believes in the same things that you do.
Also consider your risk factors, not just travel / classes / shows. If your dog will routinely be exposed to wildlife like racoons, bats, skunks, rabbits, ... then the risk is much higher for illness. Also if your dog will be in contact with many other dogs such as dog parks or must be walked to eliminate several times each day...you don't know if other dogs who frequent the area are carriers (not vaccinated) and their waste is potentially infective as well. Lastly, there is always the legal issue if your dog ever bites someone and you cannot prove a current rabies vaccination. And most bites are not to strangers. I would consider who the dog will be in contact with, in your own extended family...children, elders, relatives who may be fearful of dogs already. You will have to surrender your dog to various fates, depending on the laws in your area, if a dog bite is ever reported.