If trying to finish an M26 on a very limited budget, I would start by priming the entire model with a spray can of flat black. This is the most important coat of paint. It needs to cover everything. I would make multiple light passes at a distance that allows the paint to reach the model while still wet. Keep the aim point moving. Do not flood the model. Do not hold the can back so far the paint arrives dry. I would let the paint dry between coats. I would shake the can thoroughly before each application. I would always start spraying off the model to avoid getting any splatter on my model. I would check the nozzle regularly to make sure it is clean. A dirty nozzle produces splatter.
If you just cannot get black primer into a deep recess. hand paint that. I might even hand paint recesses before priming.
With the primer coat down, I would now spray my olive drab from a can exactly as described above with one exception. I would not try very hard to get the paint into all the recesses. I would let the paint naturally accumulate on high points. This will result in a contrast paint coat with light and dark areas of olive drab.
Once that is dry, I would detail paint the tank by hand. Go slow. Use a fine brush. Acrylics are really good for this step because if you mess up, a quick swipe with a brush wet with water will clean up most of a mistake.
Next, I would apply decals. Here you have two ways to go.
Method 1: Gloss coat the model using a spray can. This does not need to be thorough. You just need to get the spots where you intend to put a decal. Those spots need to be nice and glossy smooth. Let this coat dry completely. Gloss anything takes longer to dry than flat anything. Once dry, add the decals. If you cannot afford decal setting solution, use white glue. If you need to put a decal on a complex surface, you will need to invest in a decal softening solution.
Method 2: Skip the gloss coat. Paint white glue onto the back of each decal and apply it. Push it down with a wet brush. Get all the air bubbles out. Clean off any white glue that squeezes out the back. Again, for complex surfaces, a decal softening solution will be required. This method may not work so well over complex surfaces.
Once the decals are on, spray the whole model with a flat clear coat from a can. Use the directions above. Do not flood the model. Let the clear coat dry between coats. Do your best to get a uniform finish.
At this step, if I had some money, I would invest in some oil paints and mineral spirits–burnt umber and light mud. I would do a pin wash with the umber and some mud effects with the mud color.
Next, I may need another flat coat. I may not. No oils means no need for a second flat coat.
Now I can do some pigments. Take a pencil and run the lead on a piece of sandpaper. That is the pigment for the machine guns. Purchase a cheapo set of pastel colors. Grind up the browns and grays on some sandpaper, then apply the resulting fine dust.
Once all the artful dust is on the model, stop handling it. It’s done.
There are some other things that can be done along the way. Soil from the garden can become dirt on the model. I recommend putting the dirt in the microwave for a few minutes to kill all the creepy crawlers. Do not let your girlfriend, mom, or wife catch you doing this.
If any decals silver, you can pop the air bubbles and paint over them. You can put some pigment over them.
You can do some spattering with mud colors. Run a brush wet with paint against a toothpick. Instant splatter. Do not over do this.
You can do some more spattering with mud colors and an old piece of sponge. Blot the sponge in some paint. Blot most of it off. Press it against your model. Do not over do this.
Acrylic and oil paints can be used for all sorts of rust effects, rain streaks, and general dirt deposits with some artful application.
You will need to accept that you are learning and this will all be a series of experiments. You may not get things right the first time. Play with it. Have fun. Do your best. Use what you learn to do better on the next one.
Finally, welcome to the forums!
Edit: Please note, I am a very mediocre model builder. The above is a thought experiment based on my own experiences. It assumes a very small budget for paints and supplies. One of the better model builders will probably have different advice for you. I have seen YouTube videos of pretty good model builds done on a budget. In some of those, the model builder hand paints everything using paint-by-number style paints that come with the kit.