You have already purchased the Quicksilver mid mono amps. You need to let the amps break in along with the tubes. I would not worry about changing tubes until they are broken in and you get use to the overall sound of the amps. Learn to bias your amps and check the bias often as the new tubes break in.
Different brands of tubes will sound different but will not change the basic sound of the amp. No set of tubes will make a Conrad Johnson amp have a similar sound to say an Audio Research amp. You can use different tubes to fine tune the sound. Normally you choose an amp that you really like the sound of and that works well with the rest of your system. Then you can roll tubes to fine tune the sound.
In general El34 tubes will not produce quite as much power as the 6550/KT88/Kt90 type tubes.
The El34 type tubes will give you a different sound then the 6550/KT88/Kt90 tube types. Different brands of EL34 tubes will sound slightly different. The same is the case with the 6550/KT88/Kt90.
It is always good to have a set of spare tubes. I would not worry about selling tubes right now. Get to know your amps and make sure they are a good fit with the rest of your system