Gary, as you have difficulty understanding the spec sheets and circuit function, you should not join bits and pieces of other designs because the number of connections match.
Use the internet, choose a pilot project, with less dangerous power levels.
1) Execute the project;
2) Obtain functionality;
3) Understand the basic function and the component working conditions;
4) Intelligently tweak things slowly and note the results;
5) This enhances your understanding of circuit function and how the components will respond;
6) To meet your established goals; start doing 'upgrades' of the high power section calculating for power dissipation and loading in EACH component before replacing anything. It's a balancing act among function, power handling, cost, size, operating conditions, efficiency, reliability, stability. This list can grow if you want to institute ROHS materials, EMC, BOM reduction et al. Don't rush this.
Gary, as you can see, reading and understanding a spec. sheet or app note is key to a lot of these parameters. If the language and diagrams and charts used are difficult for you it means you have some fundamentals you need to digest first.
You must be familiar with theorems, units and formulae based on names like Ohm, Faraday, Maxwell, Thevenin, Kirchoff, Watt, Joule, Coulomb, Ampere, Volt, Henry, Farad,.........etc.
Thermodynamics basics for assessing forced air or water cooling is also useful.
Then you must be familiar with the materials and methods components are made with in order to spec them. eg. Silicon, gallium arsenide, SiC, carbon, carbon film, ferrite, iron, mylar, ceramic; epitaxial, trench, trench/epitaxy, wire wound, sintered, laminated,.. this list is sizeable......
For instance, you can purchase a silicon bipolar transistor with similar specs in terms of main specs such as Vce, Vbe and such. BUT one may be made for audio work (epitaxial) and one is a good switcher (BISS). You must be able to determine this from the spec. sheet, it is critical. If you have good fundamentals you can establish/change operating conditions to make viable part substitutions being aware of their specs.
Now there are tools to help you. For quicker development use a simulator such as LTSPICE (free) or PROTEUS ISIS or Multisim blue (free from Mouser). In a sim. you can 'try' out ideas and easily 'measure' outcomes and then determine if your parts can handle the loads placed on them. A LOT of the calculations are done for you and results are displayed graphically. Sims aren't perfect but they can automate lot of the time consuming design work.
In my experience about 50% of the time you can go from a sim. schematic to a working prototype with no tweaking. Usually the tweaking comes from having taken short cuts like using ideal components (inductors) rather than real world models. If you take the time to acquire/make the real world models your sim is quite realistic.
Take it one step at a time and sidestep the frustration dude. You have bitten off too much IMHO.