It depends, that's why I've sprinkled my replies with words like "generally" and "maybe." Certainly if a soldier POP is not getting its Life Needs it is likelier to join a rebel group. However, it's CON may be high too and you may just be hostage to greater desire for political reform. Keep in mind in this game that sometimes past decisions take some time to have effects on POPs and how they develop desires, etc. If you can keep plurality and CON low for some time you may get lucky and find POPs more desirous of social reforms, thereby allowing you to retain a more controlling state (if that's what you want).
It will take time to increase your soldier POPs. Try to diversify where you recruit soldiers from in order to not put too much of a burden on one state. That way when you suffer casualties your whole army won't be undersupplied for soldiers. Also, depending on who your enemies are you should be able to build up a smaller, high quality standing army supplemented by your mobilized reserves (what's your mobilization pool?). In recent games as Germany I've probably had a standing force of some 10 30,000-men armies (100 brigades). That, in addition to my reserves was more than enough to deal with France or Russia (I loathe mobilizing, if only because it means organizing so many brigades). I've fended off both opponents at the same time with reserves - it's all about how you pick your battles. You're not too far off from that with 70 brigades - just be patient.
Do you have an immediate goal for which you need the soldiers? If you've just recently united Germany you can probably hold off a few years while you consolidate your gains.