You can, and it works better than most people expect. The hard part of speaking is pulling words out of your head fast enough, and that is something you can train alone. The one thing solo practice cannot give you is correction, so plan around that.
Less time than the fluency guides suggest, because travel does not need fluency. The survival phrases take a weekend. Comfortable tourist Spanish takes a couple of weeks of daily practice. Fluency is the thing that takes months to years, and you do not need it for a trip.
Football in Spanish runs on a small set of phrases fans say without thinking. Learn the reactions, chants, and after-the-match lines whole, and you can follow a game and talk about it with only a little Spanish.
Fewer than you think. The most common 800 to 1,000 words cover most everyday conversation. But the word count is the wrong thing to count, because conversations run on whole phrases you can say without thinking, not single words you assemble on the spot.
You understand more than you can say because understanding and speaking are two different skills. Understanding only needs you to match what you hear; speaking forces you to produce whole phrases cold. You close the gap by practicing out loud, not by understanding more.
You freeze because recall under pressure is a separate skill from knowing the words, and it collapses when you have no ready-made phrases to fall back on. The fix is rehearsing phrases out loud until they're automatic.
You stop translating by rehearsing whole phrases out loud until they come out without the English step. It's a stage you outgrow with reps, not a habit you can think your way out of.