Upon coming back I couldn't reassemble a squad.
Whenever I see this I feel obligated to check if you're playing the version in the sticky at the top of the forums (which was released earlier this month), or the version on the main Bay12Games site (which was released four to six years ago). The reason for this is that somewhere in the years between those two releases, help text was added to explain how to assemble your squad; this question used to come up all the time.
The method for assembling new squads is pretty arcane; you press 'R' to Review Liberals, then press 'Z' from that screen to form a new squad. Press the letters associated with the Liberals you want in your squad, then press enter. You'll be prompted to pick a squad name, and then you're good to go.
For your next steps, I would look to recruit some additional characters and use them to fill out your squad. You can do this by talking to Liberals you encounter while visiting sites. Try to set up some fundraising (the 'A'ctivation screen will help here) and raise the money to buy weapons for your group. Practice raids by attacking the factories in the industrial district; visit the pawn shop to buy guns and sell things you steal on site.
Eventually you may want to find someone with high computers skill and use them as a hacker, then invest in a printing press so you can publish their findings. Some documents can also be found by picking up items during site actions; a thief character sneaking around is very useful here, since stealth and disguise skills will help you to avoid notice while Liberating everything not bolted down. Much safer than shooting up the entire location and risking SWAT teams showing up!