Keep your system basic and easy to set up and tear down. The less time you set up your gear to perform, the more time you have to prepare for your performance.
Many may disagree but a good basic set up is to have two speakers on two trees(speaker stands) connected to a mixer. Reason being, you get the majority of your audience when sound is at head level. That way the audience doesn't disapate your sound. There are variations to different methods. Don't want to turn this into a lecture..to sum up..here are combinations: 2 Passive Speakers connected to a Powered Mixer or 2 Active Speakers(built in amplification) to a passive board. Speakon rather than XLR connections because Speakon is easier to repair.
Here would be an example: Dynacord Power Mate 600 Powered mixer connected to 2 EV Speakers. simple set up. Plenty of channels to connect your instruments and your voice. Also a Powered monitor would help.
Expect to spend at least £1000. for the whole thing. You can get cheaper stuff, but to get by in a small to medium size gig, 100 people max, the minimum is 600watts. Good brand names are Mackie, Dynacord, Peavey and if you need to save some money, Yamaha. Hope this helps. JP