We do not have a control for specifying an offset every N pages in the job. If you wanted to do that (and assuming the DFE supports it which is not the case for all DFEs) then it would need to be a queue default.
The slipt sheets can be specified in FFCore using the default job ticketing
Just name sure that the page numbers in the string exceed the number of pages in the document. You should also make sure that the total number of special pages (exceptions and sheet inserts) do not exceed the limits of the DFE. I believe that limit is 1,000 for FreeFlow Print Server.
BTW> You can build the string pretty quickly with excel and a text editor:
6,12,18,24,30,36,42,48,54,60,66,72,78,84,90,96,102,108,114,120,126,132,138,144,150,156,162,168,174,180,186,192,198,204,210,216,222,228,234,240,246,252,258,264,270,276,282,288,294,300,306,312,318,324,330,336,342,348,354,360,366,372,378,384,390,396,402,408,414,420,426,432,438,444,450,456,462,468,474,480,486,492,498,504,510,516,522,528,534,540,546,552,558,564,570,576,582,588,594,600,606,612,618,624,630,636,642,648,654,660,666,672,678,684,690,696,702,708,714,720,726,732,738,744,750,756,762,768,774,780,786,792,798,804,810,816,822,828,834,840,846,852,858,864,870,876,882,888,894,900,906,912,918,924,930,936,942,948,954,960,966,972,978,984,990,996,1002,1008,1014,1020,1026,1032,1038,1044,1050,1056,1062,1068,1074,1080,1086,1092,1098,1104,1110,1116,1122,1128,1134,1140,1146,1152,1158,1164,1170,1176,1182,1188,1194,1200,1206,1212,1218,1224,1230,1236,1242,1248,1254,1260,1266,1272,1278,1284,1290,1296,1302,1308,1314,1320,1326,1332,1338,1344,1350,1356,1362,1368,1374,1380,1386,1392,1398,1404,1410,1416,1422,1428,1434,1440,1446,1452,1458,1464,1470,1476,1482,1488,1494,1500,1506,1512,1518,1524,1530,1536,1542,1548,1554,1560,1566,1572,1578,1584,1590,1596,1602,1608,1614,1620,1626,1632,1638,1644,1650,1656,1662,1668,1674,1680,1686,1692,1698,1704,1710,1716,1722,1728,1734,1740,1746,1752,1758,1764,1770,1776,1782,1788,1794,1800,1806,1812,1818,1824,1830,1836,1842,1848,1854,1860,1866,1872,1878,1884,1890,1896,1902,1908,1914,1920,1926,1932,1938,1944,1950,1956,1962,1968,1974,1980,1986,1992,1998,2004,2010,2016,2022,2028,2034,2040,2046,2052,2058,2064,2070,2076,2082,2088,2094,2100,2106,2112,2118,2124,2130,2136,2142,2148,2154,2160,2166,2172,2178,2184,2190,2196,2202,2208,2214,2220,2226,2232,2238,2244,2250,2256,2262,2268,2274,2280,2286,2292,2298,2304,2310,2316,2322,2328,2334,2340,2346,2352,2358,2364,2370,2376,2382,2388,2394,2400,2406,2412,2418,2424,2430,2436,2442,2448,2454,2460,2466,2472,2478,2484,2490,2496,2502,2508,2514,2520,2526,2532,2538,2544,2550,2556,2562,2568,2574,2580,2586,2592,2598,2604,2610,2616,2622,2628,2634,2640,2646,2652,2658,2664,2670,2676,2682,2688,2694,2700,2706,2712,2718,2724,2730,2736,2742,2748,2754,2760,2766,2772,2778,2784,2790,2796,2802,2808,2814,2820,2826,2832,2838,2844,2850,2856,2862,2868,2874,2880,2886,2892,2898,2904,2910,2916,2922,2928,2934,2940,2946,2952,2958,2964,2970,2976,2982,2988,2994,3000,3006,3012,3018,3024,3030,3036,3042,3048,3054,3060,3066,3072,3078,3084,3090,3096,3102,3108,3114,3120,3126,3132,3138,3144,3150,3156,3162,3168,3174,3180,3186,3192,3198,3204,3210,3216,3222,3228,3234,3240,3246,3252,3258,3264,3270,3276,3282,3288,3294,3300,3306,3312,3318,3324,3330,3336,3342,3348,3354,3360,3366,3372,3378,3384,3390,3396,3402,3408,3414,3420,3426,3432,3438,3444,3450,3456,3462,3468,3474,3480,3486,3492,3498,3504,3510,3516,3522,3528,3534,3540,3546,3552,3558,3564,3570,3576,3582,3588,3594,3600,3606,3612,3618,3624,3630,3636,3642,3648,3654,3660,3666,3672,3678,3684,3690,3696,3702,3708,3714,3720,3726,3732,3738,3744,3750,3756,3762,3768,3774,3780,3786,3792,3798,3804,3810,3816,3822,3828,3834,3840,3846,3852,3858,3864,3870,3876,3882,3888,3894,3900,3906,3912,3918,3924,3930,3936,3942,3948,3954,3960,3966,3972,3978,3984,3990,3996,4002,4008,4014,4020,4026,4032,4038,4044,4050,4056,4062,4068,4074,4080,4086,4092,4098,4104,4110,4116,4122,4128,4134,4140,4146,4152,4158,4164,4170,4176,4182,4188,4194,4200,4206,4212,4218,4224,4230,4236,4242,4248,4254,4260,4266,4272,4278,4284,4290,4296,4302,4308,4314,4320,4326,4332,4338,4344,4350,4356,4362,4368,4374,4380,4386,4392,4398,4404,4410,4416,4422,4428,4434,4440,4446,4452,4458,4464,4470,4476,4482,4488,4494,4500,4506,4512,4518,4524,4530,4536,4542,4548,4554,4560,4566,4572,4578,4584,4590,4596,4602,4608,4614,4620,4626,4632,4638,4644,4650,4656,4662,4668,4674,4680,4686,4692,4698,4704,4710,4716,4722,4728,4734,4740,4746,4752,4758,4764,4770,4776,4782,4788,4794,4800,4806,4812,4818,4824,4830,4836,4842,4848,4854,4860,4866,4872,4878,4884,4890,4896,4902,4908,4914,4920,4926,4932,4938,4944,4950,4956,4962,4968,4974,4980,4986,4992,4998
