Sorry if that sounds a little bit harsh. But in my opinion your level of understanding about the bits and pieces of multirotors are a bit too little to build a multirotor from scratch. In my opinion you should look after setups people have build and are flying with no problem like
David Windestål's tricopter design. Yeah I know there are some parts which are backordered right now. But I would advise you to order them anyway. They will probably get in stock in the timeframe of the next 3-4 weeks and after another 2 weeks of shipping they will be at your place.
If you cannot accept that there are 3 possibilities. One is you look for other setups and look if all parts of them are in stock. Second option is you look after alternatives for each item. And third is you take much more money in your hands and buy a ready to fly multirotor.
Nobody can decide for you if you want to have a tri or a quad,
which dimensions the booms should be
and which design you want to have for template.
All that is important as is it does decide how much weight the multirotor will have when flying.
And thats a need to know if you look for the motors and props because they will have to lift this weight at a certain amount their power.
Hell I already fly my tricopter since some hours and have read much about them but it would still would not be easy for me to do a multirotor from scratch that has a good chance of being a good multirotor.
And all that needs hours of work looking for every part making calculations how the weight changes and if the fitting parts are in stock....
I don't think that anybody can do this for you in the near future. Because of that look out for already flying setups and build after them without changing many parts.