If your Gov't TSP is this one;
http://www.tsp.gov/ it looks as if they are not currently matching any part of your contributions. (see this page;
http://www.tsp.gov/uniserv/features/chapter04.html )
"As of the date of this Web edition, matching contributions had not been authorized by any of the uniformed services. Your service will notify you if you are eligible to receive matching contributions." Basically, that sucks cause one advantage to a corporate 401(K) is the employer matching part of your contributions. Essentially free money.
Check and see if they are indeed matching the percentages mentioned. Even if they aren't, one advantage to a plan such as this is that it has a much higher maximum contribution limit than an IRA. Also, look CAREFULLY at the investment choices you have made and seek the advice of a professional to determine whether or not they are appropriate for your situation. If they are matching then great. If not, consider alternatives. Again, professional advice is paramount.
If you can afford to put 25% of your salary away then do it by all means but make sure you are doing it in such a way that as much of it as possible grows tax deferred (An IRA is a perfect example but they have limitations that may not suit you - $4000 annual limit for contributions, for example. A Roth IRA also has a limit of $4000) and that you invest - again - in instruments appropriate for your situation.
Post #1 makes an excellent point. Putting as much as you can toward your down payment and getting the shortest term loan you can afford helps build equity quickly. One of the best ways to build wealth is through home ownership.