I always recommend ball bearing blocks as the extra cost is small but the friction reduction is huge.

The loads on the genoa will be similar to those on a monohull. The mainsheet loads will be higher due to the bigger roach. The more purchases you have the more friction and the more rope you need to pull in or release.

So taking one of my trailable designs (Strider/Wizard etc) as an example

A beach cat with the same mainsail area may have an 8:1 purchase but that is generally too much on a Wizard. 4:1-6:1 is optimum. Barton (see below) Size 3 blocks are good for the mainsheet, size 2 for spi and genoa. 25mm genoa track. Size 1 for mainsheet track.

As far as actual loads are concerned I always work it this way. I can just lift my own weight, 75kgs, so a 4:1 purchase would be 75x4 or 300kgs. If the load was more than that I wouldn't be able to pull it in, or release it. So it's the boats way of saying it's overpowered. I try to use thinner ropes than most as again it's less friction and obviously less weight. So 8mm for the mainsheet and maybe 8 or 10 for the genoa sheets.

I have used 6mm on spinnaker sheets but they are hard on the hands (even though I always wear gloves) and stretches more. So again 8mm is more comfortable, but thinner is better in light winds

I find cleats on the traveller car itself better than cleats on the track ends.

I tend to use Barton deck gear www.bartonmarine.com as Barton offer good value for money, have a big range and are helpful with answering specific questions. They cover all boat sizes up to about 40ft/12m.  Readily available in Europe they also have stockists in Canada and the USA (see their website for a full list)