When custom ordering you should be able to request the heavier head weight without having to purchase a weight kit.  I would suggest working with a qualified fitter to help you with determining how heavy you want the head to be.

Going a little heavier seems to always be a safer play but the best part is that the weights are changeable so in the end you can experiment...I would agree that you should consider finding a fitter with various weights to see the differences...

IMHO

Yes, you can request for the heavier weight. If you want heavier weight for 35 inches putter that available at Titleist factory are the 15 grams and 20 grams. If you want more heavier weight than that then you should order them through Scotty Custom Shop.

If I remember correctly you can custom order the putters to a specific weight.  I order a GOLO a few years back and wanted it heavier.  When I got it, the shaft had a different label that said heavy.  The length, weight and swingweight were all hand written on that label in silver sharpie.  I thought it was pretty cool.  I would just go to a verified Scotty dealer and ask them to place the order for you.