This is my very first year doing a light display with controllers. I did quite a bit of research, watched countless videos, done some proof of concept testing and all because at the beginning of this month I decided I wanted to try this.

I was hoping to get some feedback on my overall plan as well as some of the details. Every year I've only ever done warm white lights. So it's what I have the most of. I'm really trying to do this on a budget, so I think most of my new light purchasing will occur after the season is over.

Here's my general setup:
Vixen 3
2 - Arduino Based controllers using 2-8 Channel Sainsmart Mechanical Relay Boards each (16 Channels per controller)

I have all of my normal lights that I put up every year: icicle lights, column wrappings, two 20 foot trees that I wrap, quite a few bushes that get netted
And this year I'm adding 8 24" mini trees, which I've already started building.

The plan is to build each one into a CG-1500 box using extension cords, (like the light o rama setup). Because outlets seem like a less efficient use of space and won't easily be weather proofed.

Here are some of my questions, I understand the SSR are the standard for a cheaper build, however, while next year I'll probably do those - the mechanical relays are well under $10 for a 8 channels delivered in a few days. And because I waited until November before I decided to do this, sourcing overseas won't allow them to arrive in time.
But, what are the limitations or problems with using mechanical relays instead?

As far as using extension cords out the bottom instead of outlets, is there anything I should be worried about or be concerned about? I'm going to be wiring the to terminal distribution blocks to keep them mounted and then use strain relief brackets to insure they won't get ripped out of the box.

Please let me know if there is anything I should be concerned about, or if there's anything that I didn't consider?

Sorry this is so long, this is my first post in this community.