I’d do what you are doing: hire a (presumably cheaper) person/ firm to do tree trimming and shrub removal. As long as you and/or they have good knowledge and experience of how to accomplish this successfully.

It is perfectly fine to present a designer with a cleaner slate. That will get both of you closer to what you have in mind.

It depends on what you have done. I've seen trimming that I've profoundly disagreed with and had wished the owner got trimming counsel from the designer before having it done. It's not as though there is a single approach that is always right. Also, when it comes to getting landscaping done, there are many quality levels. You need to find a designer (who might also be the landscaper, but maybe not) whose work spins your beanie. Just because you hire a landscaper doesn't mean that the tree work must be included in his contract (if it's a big price difference.)

In spite of that, chances are that whoever does your tree work will do an acceptable job and there will be no harm done. I'm just saying that it's not a guaranty. you have to understand and control the outcome.

From a cost POV, yes I'd agree with the approach you are taking. As a designer, I often recommend to clients that they get a "clean-out" quote from their regular gardener as I am going to charge extra for subbing that work out to someone else and having to manage them. For tree-trimming I recommend that whoever you use should be a certified arborist; for my own projects, I have a list of trusted service providers that I recommend to my clients.

This is easy. Have the design consultation first, saying you intend to remove and prune the trees and shrubs you have in mind UNLESS THEY ADVISE OTHERWISE. If you agree with their reaction, proceed accordingly.

Considering that tree removal or major pruning should be done only by an experienced, certified arborist (with appropriate licensing and insurance), I can't see how the cost would change signficiantly whether or not you hired them directly or they were recommended by the designer. A properly trained and experienced arborist is not cheap regardless of how they were sourced!!

I typically operate in the manner kitasei describes. I suggest removal or major pruning work as part of my initial site consultation and expect that it be fully accomplished before the new landscape design is implimented. I also provide referrals IF the homeowners do not already have a qualified professional in mind.

If you find that your tree people are charging significantly less than others recommended, chances are very good you will be receiving significantly less skilled work. This is not an area you want to cut expense corners on!!

As a designer, I'd recommend starting with a company that specifically does the tree work first. Better to work with people that are experts in their area of focus. Then I highly recommend working with a local designer to help you bring your ideas together. And having the tree work done ahead of meeting with the designer will give them a clearer picture of what they are working with. Good luck with your project!

James