I started some HRT of 250mg Sustanon EW, about 6 weeks ago. I didn't have any HCG at the time but I do now, is there any point in starting it now, or is it to late?
Am I missing something here? If this is HRT, as you say, this is not a cycle; it is a "life" cycle. HRT implies replacement for life. Low dose test and, sometimes, GH, for life.
That said, the reasons for using hcg are different. If you do choose to use it, low dosages are fine, even 250iu every 5 days would probably suffice. It's implied that your Leydig (test-producing) cells are already dysfunctional, and rendered unecessary by the exogenously-administered Sustanon. If you are still interested in fathering children, perhaps you may be interested in preserving Sertoli (sperm-producing) cells, but that's about it.
During a (non-"HRT") cycle (i.e. typical gear head cycle), you are using hcg to preserve both Leydig and Sertoli cell viability and to quicken the recovery of your own endogenous test levels upon termination of the cycle.