What I would do different if I had to do it all over again.

A.K.A. What I Learned and Advice I would give

The first thing I would have done is emptied my garage into storage and trash. I think that it might be nice to rent commercial garage space; but the truth is that you can work on things in your garage when you can't sleep and run tests at 3 am when you are inspired to.
Next I would upgrade my tools at the very beginning. I had been thinking about upgrading my welder for better than half the project, and couldn't decide what to upgrade to, until I wore it out <home depot light welder>.
Figure out how much money you are planning on spending, you will spend a lot more, but you need to start with this base line. Using this number decide what your 'breakage' / 'being ripped off' tolerance is. For instance if someone wants to charge me $1 for a 20 cent bolt, that I need 5 of; I'm buying them. Also a set of lights that I think will work that costs $100, done. This gets extended to things like is it worth my time to pick up a nut that fell on the floor?
I would search for Open Source power supplies. Quite frankly it never occurred to me that there might be such a place. I believe that there power supply design would have worked right the first time and saved many problems.
Spec sheets lie. Not all of course, but it is important to keep in mind.
DC motor control is borderline black magic
When estimating time to complete various pieces of your project involving more than one person, be sure to add "porch sitt'n" time in. Because when you build something like this, no matter how motivated, or in a hurry you are in, people will want to talk about it, and it turns out, so will you :)
I would have gotten a commitment and paper work filled out for going to reduced hours, before my manager left and our department switched divisions.
Before I started this project I thought the guys on American Choppers were careless, suicidal, fools, for some of the things they do. Then I found myself spot welding without gloves, and said, ah I understand now. Dang I enjoyed ragging those guys.
Trying to build something like this while keeping a full time job is much harder than you think. This is do in part due to the fact that the venders and tech support that you really need to talk to work Monday - Friday. At best the places you need to buy supplies from are open till noon on Saturday.
In the SAE (English) Vs Metric debate, I would recommend metric, if at all possible. The biggest problem is that you will find yourself needing some part when home depot is open and others are not, and they will only have the SAE parts. Unfortunately I weighed the second argument too strongly and went SAE.
Contractor grade parts should be thought of as parts that you would only use on someone else's project. Contracts do projects based on lowest bid, and contractor grade fits lowest bid requirements. Further note that most nuts and bolts at places like home depot seem to be contractor grade.
Loctight holds the universe together. Our motto when assembling S.S.I.K. was 'If it has a thread it had better have Loctight!'. It comes in many different formulas, I recommend that you get 2 varieties - the first a medium strength (non-permanent) thread locking compound, the second a press apply compound (for metal surface to surface).
Note: when you remove bolts that you have applied this product to you will need to either use a new bolt, or a wire brush to scrape off the locking compound.
Duct tape may fix everything that is broken, but should never be a first resort, except for duct's that is.
Choose as few thread / nut sizes as you can. Buy boxes of nuts for all the thread sizes you are going to use. Buy bolts in the lengths that you need, plus spares of in-between sizes. If you need 8 nuts and bolts, buy 20, if you need 20 buy a box of 100.
Lead time will kill you. Make sure that you know the lead time of all critical pieces before they become critical.
Just because a web-site offers next day shipment of a product doesn't mean you will get it the next day. For everything that you need tomorrow talk with a human, early in the day, especially if you are on the west coast. This still won't solve all you problems, but at least you will have someone besides yourself to blame when the parts you need don't show up on time.
Have a fun / calming ritual. You will have failures, unexpected free time on your hands, use it well. Also if it starts feeling like work instead of fun, and your not under a deadline, go have some fun.
Invent new swear words, you are likely to run out before the project of over.

What I would do different if I had to do it all over again.

A.K.A. What I Learned and Advice I would give

The first thing I would have done is emptied my garage into storage and trash. I think that it might be nice to rent commercial garage space; but the truth is that you can work on things in your garage when you can't sleep and run tests at 3 am when you are inspired to.

Next I would upgrade my tools at the very beginning. I had been thinking about upgrading my welder for better than half the project, and couldn't decide what to upgrade to, until I wore it out <home depot light welder>.

I would search for Open Source power supplies. Quite frankly it never occurred to me that there might be such a place. I believe that there power supply design would have worked right the first time and saved many problems.

Spec sheets lie. Not all of course, but it is important to keep in mind.

DC motor control is borderline black magic

When estimating time to complete various pieces of your project involving more than one person, be sure to add "porch sitt'n" time in. Because when you build something like this, no matter how motivated, or in a hurry you are in, people will want to talk about it, and it turns out, so will you :)

I would have gotten a commitment and paper work filled out for going to reduced hours, before my manager left and our department switched divisions.

Before I started this project I thought the guys on American Choppers were careless, suicidal, fools, for some of the things they do. Then I found myself spot welding without gloves, and said, ah I understand now. Dang I enjoyed ragging those guys.

Contractor grade parts should be thought of as parts that you would only use on someone else's project. Contracts do projects based on lowest bid, and contractor grade fits lowest bid requirements. Further note that most nuts and bolts at places like home depot seem to be contractor grade.

Duct tape may fix everything that is broken, but should never be a first resort, except for duct's that is.

Choose as few thread / nut sizes as you can. Buy boxes of nuts for all the thread sizes you are going to use. Buy bolts in the lengths that you need, plus spares of in-between sizes. If you need 8 nuts and bolts, buy 20, if you need 20 buy a box of 100.

Lead time will kill you. Make sure that you know the lead time of all critical pieces before they become critical.

Have a fun / calming ritual. You will have failures, unexpected free time on your hands, use it well. Also if it starts feeling like work instead of fun, and your not under a deadline, go have some fun.

Invent new swear words, you are likely to run out before the project of over.