I usually hesitate before answering questions like this because there are so many variables hidden within that simple request for advice .
I also hesitate to answer these questions because there are some very knowledgable experts here and I'm far from one of those .
But I saw your post and thought " what the Heck "

I am not a commercial leather sheath maker , it is purely hobby and not financial for me , so I think I can maybe add a few answers to your questions that come from a working on your kitchen table , flying by the seat of your pants , adapting tools to answer a need , what have I got to lose point of view .
Your first sheath will probably not be a work of art , but there is no reason why it can't be a clean , well designed , functional sheath that gives a pride of ownership and the ever important desire to improve on the next one .
There are so many tools and gadgets in the world of leatherwork that it can be very deceiving to a newby about what is required .
I personally work with a ridiculously small limited selection of tools and still somehow manage to turnout a sheath that is totally usable and functional .
Apart from the leather , needles and thread , contact adhesive , leather dye you will probably already have all the things in your household that you need to produce your first sheath . A few of the required tools you need are easily adapted from other tools and objects that you will already own or can be pushed into service the way they are . These are not ideal , but I guarantee they will get the job done .
No it won't look like some of the beauties you see pictures of here by the experts , with tooling and embossing etc , but it will still be something to be proud of .
Don't spend money on things you don't need when your first starting out , keep it simple and you will be amazed at what can be achieved .
What sort of knife do you have , that will determine what weight of leather and the design etc .
Give us a bit more info , and I'm sure the experts will contribute .
It's like when I was young and used to run to get fit for football . I used to tell people the hardest part of training was getting motivated to put my running shoes on . Once you got going the running was easy .
It's the same with leatherwork , buy a piece of leather and a handful of other things and make that first sheath , the others will be easy after that
Ken