Tvheadend

I'm using TVH 3.4.27 on OpenELEC 3.2.4 with a Skystar HD2 DVB-S2 card.

The adapter is configured using these settings:

ter0_STB0899_Multistandard
{
        "enabled": 1,
        "fe_path": "/dev/dvb/adapter0/frontend0",
        "dmx_path": "/dev/dvb/adapter0/demux0",
        "dvr_path": "/dev/dvb/adapter0/dvr0",
        "type": "DVB-S",
        "displayname": "TechniSat SkyStar HD2",
        "autodiscovery": 1,
        "idlescan": 0,
        "idleclose": 1,
        "skip_checksubscr": 0,
        "sidtochan": 0,
        "qmon": 0,
        "poweroff": 1,
        "nitoid": 0,
        "diseqc_version": 0,
        "diseqc_repeats": 0,
        "extrapriority": 0,
        "skip_initialscan": 0,
        "disable_pmt_monitor": 0,
        "full_mux_rx": -1,
        "grace_period": 0
}

By disabling idle scanning I presumed that the adapter won't be used until it's actually used by a viewer or recording (after the initial scan completes - of course) - but that doesn't seem to be the case. TVH still tunes to muxes/transponders - apparently to update EPG data.

TVH found 1658 services on 109 muxes in total (Astra 19,2E). But I'm actually using only around 40 mapped services/channels. Because I didn't want TVH to grab useless EPG data I unchecked the checkboxes in the "EPG" column in the services table for every service I don't use (which obviously took some time ;)).

But TVH doesn't seem to care about that in the way I expected, because it's still tuning to muxes/transponders I don't even have one mapped channel on. After that it seems to start all over again and again and again...

The only way to stop this is to disable the "EIT: DVB Grabber" entry (which is the only one I've enabled) - but then of course, there is no EPG data updating at all. What I want is to update the EPG data maybe every 24h, 3d or something like that.

My questions:

1.) Is there a way to tell TVH to update DVB EPG data only once in a given time period? Or to update only if the service is actually in use (which would produce gaps, of course)? I found a "Grab interval" setting - but as far as I understand this is only for XMLTV?

2.) Shouldn't the disabled "idle scanning" option also prevent TVH from (continuously) updating EPG data (seems a little bit illogical to me?)?

3.) What is the "EPG" checkbox in the services table actually for?

4.) The effect of the "Enabled" checkboxes for muxes and services isn't entirely clear to me. If I disable a mux or service - does this mean, that TVH will ignore this mux completely (= never tune to it again)? Could this be a away of limiting EPG data updates?

5.) Wouldn't it be a good idea to have an option to grab EPG data for actually mapped channels only?

Thank you very much for any help on this topic!