"Which DAW do you think is best?" To that I have to say Reaper. It's enourmously powerful, especially for the low price of their software, which you can choose to evaluate forever should you wish to, or rustle up £60 for a Reaper licence, free updates for the foreseeable, feature-rich, easy to start.
"Which free plugins are really worth having?" All of them, why not?
But seriously, some free plugs are as sonically capable as the paid tier ones. Here's some that I've used for a while and still enjoy their sound:
- Valhalla Super-Massive (delays crossed with reverbs, some of which are huge with long tails). Cost: Free. VST. They have a whole range and give them all away.
- Crio. Mono synth with nice sounds, Distinctive tones, great for acid styles. Cost: Free. VST.
- Bitsonic Gnat. A worthy free synth VST, see above.
- Speed Drum. load it up with sample sounds, it works as well as NI Battery, with admittedly fewer slots, but it's free and still has enough. VST. -