Salsas, Sauces and Crema

It is off-season and fresh tomatoes where I live are genuinely bad right now — pale, mealy, no flavor. I want to make a cooked red salsa but I do not want to use bad fresh tomatoes just to feel authentic about it. Is canned an acceptable substitute and if so which type works best?

My fresh salsas and hot sauces go bad within five or six days in the fridge. I make a batch, use it twice, and by the third time it has gone off. I want to be able to make a larger batch and have it last two to three weeks. What do I need to do differently to extend the shelf life without processing it in a full canning setup?

Every recipe I find gives different ratios and I cannot figure out if there is a baseline or if it is always just to taste. I want a starting point I can adjust from rather than being completely at sea every time. Is there a standard ratio for a red salsa that I can use as a baseline?

I have seen burritos with one salsa, burritos with two, and once a burrito that had three (a green, a red, and a pico). Is there a principle for how many salsas work in one burrito and whether combinations work better than a single good salsa?

My salsa is always either too chunky or too watery after blending. When I try to get a smooth consistency I run the blender too long and end up with a thin, frothy texture that does not coat anything. When I pulse it the chunks are too large. Is there a technique for getting a smooth but body-having salsa from a blender?

I have been to places that put cold salsa straight from the fridge into a burrito and others where the salsa is clearly warm. I have also noticed that my own burritos seem to taste different depending on the salsa temperature, but I cannot tell if that is the temperature itself or just what that particular salsa tasted like. Does salsa temperature inside a burrito actually matter?