I'm having four issues when baking bread...

Without meaning to dampen your enthusiasm, let me say that most of us spend our spare time scouring the forums or baking or posting specifics.   For a start I'd begin at the beginning by reading through the lessons.   Or read the blogs to get some background.  All your questions are commented on time and time again - just not specific to your case.  What you want is possible.  What you need is research and practice.  I haven't been baking long but Thx to the TFL community I am baking successfully.  You will too with an investment.

Read about leaven and retarding for flavour - even flour choice - and baking methods for crust manipulation And additives and  effect on final product.  Post a pic and a recipe and ask specifics.  You will get feedback. 

Invest in your skill and go for it!

Study bread baking with an expert the way real pros do it:  go to school or at least buy a text book and read it.  If and when you do that all your questions will be answered and you won't have to try to decide which answers on The Fresh Loaf are right or wrong because your expert (the author of the text book) will provide the answers as the pro he or she is.  Many want to learn to bake bread without taking a lesson, thinking that a cookbook's good enough.  I disagree.  Cookbooks are a list a recipes with some lessons thrown in, maybe.  The Bread Baker's Apprentice is an example.  It's great but it only goes so far.  Look at real text books.  They start with the foundational material and build you up, giving you the information in a gradual way with practice sessions and questions based on the chapter  just read.  A textbook is what pros use; why not you?

Look at these two as examples:  DiMuzio's Bread Baking and Hamelman's Bread.  You might find them in your local library.  Both are available at Alibris or Powell's books, at times.  No need to buy a new one much.  Do so if you want, of course.  But choose one and bake your way through it.  Take your time.  What's your hurry?  By the end of a year you'll know more about bread baking than you will by using any other way, even The Fresh Loaf to get your answers. 

I've been baking for decades now.  I learned a lot from cookbooks but every time I took a course or read a textbook I learned so much more quickly and was always surer of the truth of the answers to my questions.   Because of that I had MORE FUN learning.  What could be better?  I sure wish I'd started that way.

tell us about where you are in the world and what kind of breads do you see at your local bakery?  

Tell us about the flour you are using?  What is your traditional bread?  

I agree with the others that you are missing the basics.  To answer your Q's 

1) The dough has it's limitations depending on the type of flour your use.  It can only rise a certain height during fermentation before it gets tired, breaks and releases the trapped CO2 gas (the stuff that made it rise) and then falls down on itself.  What you are witnessing with bread falling is this deflating.   When the bread rises and stops it has reached it's limit.  You have two choices, either knock it down and make it rise again and bake it this time before it reaches that "stopping" level or Don't let the dough rise that high in the first place before baking it.  You do want to keep the rising crust from drying out before you get a chance to bake it.  You can figure that part of the finished volume of the loaf is achieved during the final rise, but the rest of the rise will happen in the oven when water in the loaf turns to steam, raising it more.  If you bake the loaf when it is totally stretched out, it won't rise anymore.  If it is doing that, you waited too long to bake the bread. 

2) Bakeries often have access to better and more flavourful flours because they buy in bulk and have larger choices that we do in supermarkets.  Your location will also limit your choices and so will your budget.  One simple solution for home bakers is to find a good tasting flour.  Then let it rise slowly with less yeast than most recipes.  Letting the dough rise slowly brings out flavours hidden in the flour and hidden to those who rush through the dough process. SO what does that mean?  Slow down the fermentation of the dough.  

3)  They use steam in the ovens in the beginning of the bake.  

4)  I've never seen the light brown breads at Tesco so I can't advise you on that one but check the ingredient list.  Something is making the colour.  Read the label and report back.  Yes, darker flours rise less that white ones, most of them anyway.  Good observation!  Most breads contain a mix of different types of flours and it may surprise you, as it did me, that water thinned fermented juice (yeast water) can also change the colour of the crumb, amazingly so.  Yet the flavour tends to be delicate.  Carmel colour is also sometimes added, read the label and lets hope we can pinpoint the culprit.