I feel SeeMeCNC's mounting for the towers is a weak part of their design. If you make your own delta, constrain the towers as well as possible, top and bottom. They should sit on a flat surface on the bottom, and the top plate should sit on top of them. All four sides of each tower should be fully constrained so that the tendency to lean is minimized. It should not be open on one side, or have the freedom for each tower to be a different height, as is the case with the Rostock MAX. Any sort of looseness about the areas where the towers are secured is problematic, so spend some time on designing that.
I think it would be ideal to fix the towers to four plates, two closely-spaced ones up top and another two on the bottom, ideally stacked and cut at the same time on a CNC router so that their profiles are identical. Each plate would be stood off from its associated plate using spacers, so you'd know for sure that they were set up right. Why two instead of four? Same reason the delta platform has two arms per axis instead of one. It just adds another layer of constraints, so there's less possibility for the towers to get squirrely.
I would use a Smoothieboard or a clone. Price is the same or less compared to a RAMBo, and the firmware does more things, including automatic delta calibration. Marlin and Repetier have basic bed leveling and calibration, but it's nowhere near as good. I would recommend the Smoothieboard 3/4/5X over the Azteeg X5 Mini, as it has big, beefy power FETs for the heated bed and hot ends. I blew the bed heat FET on an Azteeg X5 Mini, which is just a weak, tiny, surface mount part. That's no way to do a bed heater!
Put the bed heater on wood, and rest the wood on FSRs, one near each tower. That way, you can calibrate without needing a separate Z-probe, and it will be accurate to the exact position of the nozzle.
Consider using a
fishing line drive. They can be a little fiddly, but the cost per inch on fishing line is perhaps 1% of what it is for GT2, and it gives you options for how the motors are mounted that you wouldn't have otherwise. The link goes to what I think is the best implementation, with the line being passed between the pulley on the stepper and another pulley close by. This provides enough friction to keep the line from slipping. The other (easier) design is to have the thread go to a single spool on the stepper, but that lets it wander up and down the spool as the carriage moves up and down, so you don't get constant tension. In either case, the SeeMeCNC tensioning solution (pulley mounted to slots in the tower tops) is a good way to tension the line - and it will need tensioning!
Use an E3D, and put three of SeeMeCNC's tiny squirrel cage blowers in fan ducts for part cooling. In fact, I would say to just use the SeeMe effector, since you'd have instant compatibility with dozens of existing mods. You'd also be able to use Trick Laser arms out of the box. STLs are out there, so you can just 3D print the effector if you don't want to buy it from them.
For my effector wiring, I used cable made specifically for robotics applications,
like this. It's designed for continuous flex, is shielded, and can be had with many conductors, so there is just medium-thickness cable running up there, rather than a bunch of skinny ones and however many zip ties. This stuff is more expensive than speaker wire, but you can have 12 conductors in one SHIELDED cable - enough for hot end heat & thermistor, +5V, +12V, GND, +5V PWM (for part cooling fan), and a Z-probe signal return wire, all in one. That gives you enough to connect all the accessories you need.
Use some nice plugs for wiring up the hot end and other stuff on the effector. I like TE Connectivity (
plug,
cap,
pins).
Take cable management into consideration from day one. Design a mast that you can run the effector and stepper wiring up. Could be a half-height extrusion sticking off the side, or a 3D printed piece that force-fits onto the structural plate below the print surface. You could also mount your extruder to it. It's important to get the extruder as close to the hot end as possible, and that would help. Alternately, you can use Trick Laser's
Fly-N-Strude mod, or my TL arm mount mod, link in sig.
It's tempting to mount the filament spool up top, and if I was designing a Delta, I might do the same. But, if you don't mind wasting some floor space, consider hanging the filament off the side of the bottom of the printer. This makes the printer less top-heavy. It also relieves the top screws and locknuts from the weight of the filament, as well as the mechanical forces of it clunking and thumping as the spool slowly turns. If you do mount the filament spool up top, make sure to beef up the top support plates and tower mounting.
and so on. 
) but that adds a servo.
(