Reserves are ONLY allowed with your opponents permission. The 1/3 system is just way simpler and less confusing than official rules. Yes, you could do it to get more cruisers... thematically there is no problem, as according to Horizon, the 12 cruiser represents the average number of cruisers in a sector, so these 'reserves' from another sector wouldn't be subject to that.
Not to mention the fact that reserves have -1 LD, a substantial enough reason not to want to take them regularly. Certain fleets are allowed to take 'types' of reserves without the opponents permission, such as Bakka being able to take Admech stuff, or Bastions taking Chaos ships. Naturally these would either count as reserves or allies depending.
Note that allies may not use fleet commander re-rolls and are subject to the 'mercenary' rule. Which means that they must disengage if reduced to 1 or 2 hits.
Races are:
IN
SM
Admech
Chaos
Daemons
Tau
Eldar
Dark Eldar
Necrons
Nids
Demiurg/Kroot
Naturally any fleet which takes vessels from a fleet list of the same race, those vessels count as reserves. Any fleet which takes vessels from another race, counts as allies. Simple as that.
I think that these two corrections (the -1 leadership, and mercenaries) work perfectly thematically, and make it less of an issue with destroying fleet lists. It still allows it to be possible if someone wanted to run a mixed fleet for whatever reason. Given the opponents permission.
Blast markers work at D6+X, I had a bunch of different options, that one worked best. D6 never really seemed like too little at 500-750 points, it always seemed about right. It's just at 1500 it's tiring and pointless when you have upwards of 50 bms on the table. After about 30 we usually don't bother placing or removing them unless they are necessary to denote shield loss.
Given the only fleet this really hurts is Demiurg, who love sucking up BMs. Although their cutting beams were not really so useful until the HA decided on the half&double thing. I might playtest it with demiurg, but I haven't taken them out of their box in a while.
Oh and RC, you are only allowed to take reserves/allies from one other list EVER. So you couldn't take say.... both Ships from the Inquisition, and ones from space marines in your IN fleet. Or reserve vessels in Bastions as well as reserves from Segmentum Solar. Etc.
On that note, you are always allowed to take reserves/allies so long as your list explicitly says so. So every fleet has access to RTs/Demiurg, Inquisition etc. You still are only allowed to take 1 ally/reserves. Which I guess would bring back in the specific inquisitors into the Inquisition doc. Basically each type would allow a different kind of 'extra' reserve to be taken..... Hrmmmm.... Meaning that with a Xenos one you could take demiurg/kroot allies as well, with a witchhunter you could take RT allies as well (but not xenos escorts). Daemonhunter would allow GK strike cruisers?
Something to think about I guess.