Lychee is another very good slicer which I think has now been updated to cover both filament and resin printing. However I personally just use Cura and Chitubox respectively, as they do a perfectly good job and I now know how to make them work for me.
There are several free CAD programmes around: Fusion 360, FreeCAD, SolidEdge,LibreCAD. What I always say is this: Tinkercad is an excellent starting point, it is pretty intuitive and you'll be producing printables in no time at all. But while its' surprising just what you can do with it, it's not as powerful as a proper CAD package and sooner or later though you will find you need something better. For me, it was when I needed to work with splines and be very precise dimensionally. This is a very important junction, because whatever software you choose, free or paid, you are going to have to invest a great deal of time to learn it and you may find (like me) that this makes you reluctant to learn another package. My advice is download all of those I've mentioned and make the same very simple object in each, then choose which one you liked most.
There is also another choice to be made, -ish: there are graphic 3D apps like Blender, DAZ3D, Meshmixer, with which you also create printables but using a more artistic (rather than engineering) approach. I can't really talk to these as I'm poor in this area.
Where you can afford it, if you're using resin I'd recommend getting a wash'n'cure type machine straight away. It just makes the whole process much less messy. It's still a wet process best done in a garage or similar (in my view). I actually use two wash tubs: one for a first wash, which gets rid of 99% of the wet surplus resin, and a second tub to rinse off the 99% clean items. I found that I got a better finish this way, as the IPA gets dirty quickly and doesn't quite leave items clean. Once the dirty IPA becomes too dirty for my liking, I clean that tub out, making the rinse tub the first wash and so on.
To be honest I haven't found a decent way to dispose of used IPA. Last summer I tried recycling it by dispensing it into clear bottles and leaving it in the sunlight for the resin particles to cure. That kind of worked but I had to filter the residual IPA and this was never as clean as new. I concluded that it just wasn't worth the effort, so this year I am experimenting with allowing the IPA to evaporate away in the sunlight, so that all I'm left with is a 75% empty bottle of cured resin, which I can treat as safe garbage. If that doesn't work I'll end up taking all the dirty bottles to our local recycling tip, where I can pour it into the huge paint tin or similar. I'd be very interested in better options if anyone has them.
As Steve says, 3D printing can become expensive. Resin more so than filament.
