I would definitely wait a much, much longer time and get a new puppy only when your current Cavalier hits a year if not two years of age. Your puppy is wonderful now, but the really tough part comes in the adolescent months. Get through that period, make sure your dog is soundly socialised and ideally get her basic obedience down pat before you consider a new puppy. I'm not saying it's impossible to raise two pups simultaneously, but it is a huge handful.
I know what you mean, when we first got Barclay we were like 'oh my gosh, he's so wonderful, lets go get his brother too!', but then he started growing up and turned into a teenager, and I'm so glad we didn't! His first birthday is on Christmas Eve, and I still don't think I'm ready to add another pup - it's so much work, and there's so much left to do yet! I don't want him to get shorted in his training, and I don't think I'm up to training two at once. I whole-heartedly recommend waiting a bit longer!
I got puppy #2 when puppy #1 was 10 months old. It's been four months now and it's HARD. Doable, but hard. I'd definately take the advice you're given here. It may seem like a long time to wait, but it'll be better in the long run.
I would also recommend waiting until you have had your current pup for at least 1 year, if not 2. Also, if you are having any problems at all with your dog don't get a puppy until they are solved. We got Allie about 9 months after we got Lloyd, and he was 17 months old. I wish we could have waited to get a second dog until we had had Lloyd longer, at least a year or more. We had to take Allie though under the circumstances, but it did set Lloyd's training back a lot. I feel if we had been able to wait longer he wouldn't have been as impressionable to another dogs behaviors. Its also a lot more work training 2 at the same time.
I think the answer depends on you and what your situation is. I did the same thing you're thinking about doing...I was enjoying Ripley so much that after about a month/6 weeks, that I got another puppy. We didn't have any major problems, it was hard work, but also fun. My husband and I had a few things going for us that helped, mainly our schedules. At the time I was only working two days per week and DH worked nights, so we were both home the majority of the day for training, not only that, but we were able to split the puppies up for training....definitely consider your schedules. The other big one is finances. I'm sure you've thought of this, but most of the routine expenses are going to come in the first year...be sure you can afford that x 2.
We waited a year between dogs, but have 4 adults living here working different shifts. We spent a lot of time with Kaz, group effort, this teamwork naturally transitioned to Gus. Schedules, notes, communication between what I guess you would call at home shifts is key. It does make for a busy life, but busy in a fun way.
Kaz is nearly a year & 8 months, barely past puppy. Gus is nearly 8 months, they are both pretty good for their age, but do have their moments. It helps that everyone is consistent in how & when they do things, daughter is a schedule Nazi. It really does take a group effort, and we would not have even considered another pup if the group didn't work so well together raising Kaz.
I figure we have another year to do of intensive communication, that is reason enough for my daughter to buy 4 calanders & a couple of planners.