A few observations. As has been said, Sig kits are great. I think anyone who is interested in the building as well as flying aspect of the hobby would do well building a Sig trainer. I can speak from personal experience about learning on a 3 channel and then transitioning to 4 channels. There are positive as well as negative aspects to this. Since most people just use elevator and aileron during flight, with occasional changes to throttle, the actual flying of a 3 and a 4 channel is identical (ignoring aerobatics). The fourth channel only comes into play during taxi, takeoff, and perhaps landing. I did need to do a little "re-learning" to get used to steering my second plane (4 channels) with the left stick during takeoff and landing. However, it was not a big deal.

So, to Michal I would say, if you like the looks of the Seniorita, build it. It's best if you have someone local who can answer questions that come up during the build. Remember to keep it light. As has been mentioned, light planes fly better. If you crash as a beginner it should be when you are going slow, and are close to the ground. This means the damage, if any, should be minimal. Since you built the plane, you will be in a better position to fix it, even if it means ripping off a section of covering to do so. You'll have spare covering, that matches. Also remember to not go crazy covering. This is your first plane. Damage is very possible, and will be possible for every plane you build. Repairs will be easier if you don't have to deal with a complicated trim scheme. Go for something with good visibility. Here's a picture of my first plane, a Sig Scamp. It had 3 channels, the wing was foam. Flew great with an Enya .15.