Since you're using MS-PL and Apache 2.0 components, you're restricted by the MS-PL license and the Apache 2.0 license. This means you can't use the GPL anyway, since it's incompatible with MS-PL, and version 2 of the GPL is also incompatible with Apache 2.0. Given that, I would suggest releasing your parts either under MS-PL, Apache 2.0, or a BSD-style, so you're not adding requirements.
You can read the licenses to see what you have to do. They aren't long. With MS-PL, you can do pretty much everything as long as everything's released under MS-PL and you include the entire license (which isn't long). With Apache 2.0, it's pretty much the same, except that you need to include any NOTICE file. You do have to include all attributions, etc., and that's pretty standard across OS licenses.
You really can't add to the licenses. You are free to put any disclaimers you want. You can put them in a NOTICE file, which under Apache 2.0 requires them to be preserved.
You should list which files are under which licenses, and you do have to include full copies of MS-PL and Apache 2.0 in the package.
Be careful about ADO.NET Entity Framework CTP4, as you say you can't find a license. If you can't find a license, ordinary copyright law applies, and you can't legally use it. You may want to write to whoever owns that code, and see what license they use.
As far as copyright ownership goes, you can never retract open source licenses for the versions you release under them, but if you own all applicable copyrights you can relicense as you wish. Some companies, like MySQL AB, released what they had under the GPL, and would sell other licenses for money, so that (say) another company could use MySQL as a part of their commercially sold product without having to release under the GPL.
Since you're using components owned by other people, you really can't do that with the entire project, but you could with your portions.
To do that, you'd have to get everybody who contributes to fill out a copyright assignment form, along with some proof that they do own the copyright (and, for example, that it doesn't count as work for hire for an employer). This does tend to diminish user contributions, so you may want to skip it entirely. You might want to look at what the Gnu project does, since they do want complete copyright, and emulate them.
Look at existing free software. They generally have a comment with a license and a copyright owner. Often, there is a list of contributors.
For example, for GCC, the file gcc/gengtype-state.c starts with
/* Gengtype persistent state serialization & de-serialization.
Useful for gengtype in plugin mode.
Copyright (C) 2010 Free Software Foundation, Inc.
This file is part of GCC.
GCC is free software; you can redistribute it and/or modify it under
the terms of the GNU General Public License as published by the Free
Software Foundation; either version 3, or (at your option) any later
version.
GCC is distributed in the hope that it will be useful, but WITHOUT ANY
WARRANTY; without even the implied warranty of MERCHANTABILITY or
FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
for more details.
You should have received a copy of the GNU General Public License
along with GCC; see the file COPYING3. If not see
<http://www.gnu.org/licenses/>.
Contributed by Jeremie Salvucci <jeremie.salvucci@free.fr>
and Basile Starynkevitch <basile@starynkevitch.net>
*/
See also this answer (to a question related to yours). The GPLv3 seems to require such comments. An example of GPLv3 code with the copyright owner same as the author is onion/onion.c from the onion HTTP server library.
Caveat: I am not a lawyer
Regarding organizations to join, you might be interested by the FSF or some free software "user" organization (like April or Aful in France; perhaps you could find the equivalent in your country).
My preference is for GPLv3 or LGPLv3 licenses.
Best Answer
The first part of Section 3 states that all contributors give you, the user, the right to use the software under whatever software patents are in effect, without any further obligations (including license fees). This applies both individually, where the contributor personally owns a software patent, and collectively, where a combination of contributed works is considered protected by part or all of a patent.
The second part of Section 3 states that, if you, the user of the software, bring suit against anyone who has a patent claim to all or part of the software, your license (and therefore your right to use the software in the manner described in the license) terminates automatically.
Collectively, these two clauses are intended to give you and the project contributors protection against patent problems, by making such protection a condition of contributing to the project or using the software.