Print at .20 res or lower if you're going to use the included pegs. If you're using M3 screws instead, then the res isn't as important.
This was designed to be printed with .5mm walls, but .4 shouldn't be a problem. More walls, the better. No supports are needed, but a brim is almost certainly required for the small pegs unless you want to gamble with the bed adhesion Gods. Don't think too much like I am :)
The tiny pegs are 3.4mm OD at the largest area and 2.8mm OD for the smaller. The holes in the bracket are 3mm and can accommodate M3 screws (if the flat is drilled out or if you force the screws in).
The pegs should fit very tightly into the holes. There's a .10mm clearance (in Fusion) which is less than my usual .20mm clearance for mating parts. If they're too tight, you may need to drill it and use some superglue.
Print time is relatively long for what it is; about 25 mins, but ehh. Maybe you can print quicker, but who knows...