Hi Bettina
Welcome to the Forum! We hope you enjoy your time here. 
There are so many ways to stimulate and teach our children, it can be a little overwhelming at first. (I felt the same way as you when my baby was first born.)
Re. your son’s prematurity, obviously every baby is different, so it’s impossible for us to say. But, yes, it’s likely that he’ll be developmentally more ready for a reading program at 6 months than 4. If you wanted to give some exploratory lessons while he’s a little younger, there would be no harm in that. Just see how he responds - if positively, keep going; otherwise, leave it a bit longer or change to a different method (actually this is true whatever the age of the child).
As to which method is best, have you read the Flash Card Method and Multisensory Method articles in the Reading section of the BrillBaby site? (I only recently rewrote those articles.) You asked about how many cards to do per day - in Flash Card Method, I have detailed the Glenn Doman method. Like you, other parents had been asking for the specific ins and outs (and now there is no need to read the book!).
If you want to compare the two methods, then check out our Advantages of Little Reader section, which looks at the pros and cons of various methods of reading instruction. By the way, you might consider giving our own Little Reader a go. At present, it is free to use! :biggrin: It has all the functionality of both flash cards and multisensory teaching - you can choose to flash cards (and can set the speed), or you can use it to show photos/videos and play sound effects. You can also customize the lessons with your own media/voice recordings, which makes the lessons so much more personal (and as your baby gets older, will really grab his attention).
Personally, I am using Little Reader and Your Baby Can Read. My 10-month-old daughter loves them both (though it took her a month to warm up to YBCR; she liked LR from the get-go). I use LR to expose my baby to Chinese, Japanese and Spanish - and I know you would like to expose your baby to Chinese and Spanish. One of the beauties of the software is that users can take advantage of file sharing. This means that you can download foreign language categories recorded by native speakers. 
Re. TweedleWink vs YBCR, the latter is specifically for teaching reading, whereas TW teaches reading, math, music and encyclopedic knowledge. I haven’t tried TW yet, but other parents have spoken positively about it. I can’t tell you much about encyclopedic knowledge - it doesn’t appeal to me personally, as I can’t see the point in filling my baby’s head full of facts. Reading, on the other hand, is a core life skill that is easiest to learn in babyhood. The ability to read fluently from a young age carries benefits into many other spheres of life because reading opens up so many avenues of knowledge.
As for Baby Einstein, I should warn you that studies have shown that babies who watch such DVDs on a regular basis actually learn fewer vocabulary words. It’s something I’ve talked about in my TV FAQs. Beware of programs that are devoid of or low on verbal content. They might mesmerize and distract (a lot of parents use them as an electronic babysitter!), but they don’t carry much educational value for babies.
As for sign language with babies, I am a big fan myself. If you’re interested, you can read about my experiences on my blog (you can click on “signing” on the left-hand side to bring up just the posts about signing). Signing is mainly about bridging the gap between when your child would like to communicate and when she can communicate verbally. Reading is a completely separate skill. Because it reduces frustration, is fun and rewarding, and gives you an amazing insight into your baby’s internal world, I would highly recommend signing.
Hope that helps Bettina, and looking forward to hearing about your experiences of teaching your son!
Maddy
PS Sapna is right - you should start with the infant stimulation cards! I didn’t try them, because I didn’t know they existed when my baby was tiny. But it explains why she was absolutely fascinated by the black-and-white photographs in our living room! lol
