Going to get help is not a bad idea and you shouldn't punish them for it... However... it is not always a good idea. so here are some ideas most already suggested I am just repeating for added support and to consolidate them.
1) make time an issue not every encounter they can plan on but on some.
2) if they have time to plan and recruit so do the bad guys.
3) information they act on to plan with changes over time. Make the enemy dynamic not static.
4) if they end up with dead hirelings then no one will work for them make reputation important.
5) conversely if they keep people alive and the rewards are good this attracts the unscrupulous (sp?)
6) Cost is always a factor
7) most people /guilds want their money up front and a reward so bleed the characters dry and no money = no help.
8) make what is going a big seceret.
additional comment - I am doing this in my game the characters are in a more or less secret war with the major bad guy organizations with the world at stake and i have them balanced with warnings that if they make it an open secret then the bad guys will have no choice to make it an open war and being evil they can do a lot outside the bounds of ethics, plagues, poisons etc they won't risk now for fear of being exposed. So even though the leaders of several nations know they aren't openly helping the characters in fear of it getting worse. I keep the game under control with real world (fantasy world anyways) reasons. It also makes for fun roleplaying when they meet the king/queen etc in secret and other agents as well.
Just a few borrowed/shared thoughts.
later
1) make time an issue not every encounter they can plan on but on some.
2) if they have time to plan and recruit so do the bad guys.
3) information they act on to plan with changes over time. Make the enemy dynamic not static.
4) if they end up with dead hirelings then no one will work for them make reputation important.
5) conversely if they keep people alive and the rewards are good this attracts the unscrupulous (sp?)
6) Cost is always a factor
7) most people /guilds want their money up front and a reward so bleed the characters dry and no money = no help.
8) make what is going a big seceret.
additional comment - I am doing this in my game the characters are in a more or less secret war with the major bad guy organizations with the world at stake and i have them balanced with warnings that if they make it an open secret then the bad guys will have no choice to make it an open war and being evil they can do a lot outside the bounds of ethics, plagues, poisons etc they won't risk now for fear of being exposed. So even though the leaders of several nations know they aren't openly helping the characters in fear of it getting worse. I keep the game under control with real world (fantasy world anyways) reasons. It also makes for fun roleplaying when they meet the king/queen etc in secret and other agents as well.
Just a few borrowed/shared thoughts.
later