This is all in my opinon so take it with a grain of salt. Longboarding is a lot about personal preferences and if you have the chance to ride a variety of gear, do it!
First and foremost get a good helmet and some slide gloves. Additional padding (elbows and knee pads) are recommended but Slide gloves and a helmet will suffice.
For downhill/free ride I'd usually go with a drop through. IMO Landyachtz switchblade line up is great for free riding and pushing is easy with a drop through. if you want more stability you cam top mount it. Any drop through will do.