You can still generate the monthly masspay files without uploading them to PayPal right away, so e.g. you could hang onto them and then just combine 3 of them into a single file to make quarterly payments. However, if your affiliates aren't earning enough to make monthly payouts (once you give it enough time to get that ball rolling), you might evaluate whether running an affiliate program is even producing enough benefit for you and affiliates to be worth the bother.
Most affiliates in our system expect to receive the standard monthly pay-outs typical of most affiliate systems that don't do instant per-sale payouts, so you should be extremely clear on your site's affiliate recruitment page that you only pay out commissions quarterly rather than monthly, and enter the URL of that page in your Seller Admin > Affiliate Program Settings > More Information URL, so affiliates can find it easily.
Generally speaking, to sort rows by a column in a spreadsheet program, you would select all the cells or columns you want to sort, then look for a Sort command that lets you pick which column(s) the selected cells should be sorted by, where you would pick the Affiliate ID column in this case. From there, you may be able to simply select the range of Affiliate Share earnings for each affiliate, which may show you an instant sum in one of the program's toolbars. We can't really provide more specific instructions for any particular software program; even for Excel, it varies depending on which version you have, and I don't even have Excel myself (I use the free Gnumeric program instead).
If you pay out commissions to any affiliate(s) by a method other than PayPal, you can edit your masspay file(s) to remove that affiliate's commission before you upload it to PayPal. We don't have any way of tracking your pay-outs to affiliates; that is entirely your own responsibility. In fact, you can disregard the IPN instructions in our Affiliate Program Settings screen, as those were intended to inform us when you pay out commissions but didn't work out as planned, so we're removing those instructions from the next version of Seller Admin.