I've been working with those numbers for a while and my most realistic model has an army of 7 divisions (3 homeland, 3 expeditionary and 1 general support) for a total of 30,00 RegF and 55,000 PRes (of whom only 50,000 are ARes). I've left of both the static base support system and CADTC training system (who should all be RegF anyway) Add in another 20,000 air reserve and navy reserve and that gets you to 75,000 PRes.
I could always push another 10,000 into a second general support div but that's as far as I can see reasonable employment as well as a solid base to expand on.
As far as home guard is concerned, I'm still floundering. Roughing it out at battalions of 500, you end up with 200 battalions per 100,000 personnel. There's no sense in adding any training or base support personnel to those numbers because those really need to be either RegF for full timers or Class A Pres for part time trainers. So the question is what can you do with 200 battalions figuring a full battalions for major infrastructure, a half battalion to minor infrastructure and maybe even companies for really small vital points. I kind of max out at 300 battalions.