1. That all depends on whether we stay configured the way we are in which case probably. Most regiments have four to six guns which are sufficient for training. On the other hand if we change our organization to deal with more artillery related tasks, then we might be able to do with less. For example, if we acquire air defence and assign certain regiments to that task then they wouldn't need guns. Similarly, some reserve regiments could be allocated to locating functions where their primary equipment is radars or UAVs. Then there's rocket. I could go on but you see the generally idea.
2. IMHO the degree of sophistication shouldn't matter as the number should be predicated on whether: a) they will be guns capable of operational use and what size of formations will we need to support, and b) how many guns do we reasonably need for training. Practically speaking, sophisticated guns are expensive and therefore we will most probably get less. Also speaking realistically, at present if we pool all our artillery regiments' personnel, we could probably fully man around 3 to 4 regiments which at 18 guns per means we could probably reasonably make use of 80 or so guns (including spares and training establishment ones.) and again assuming we will not be allocating personnel to AD, locating, or rocket.
3. The 105 C3 series is a very robust piece of kit that requires very little in the way of routine user maintenance (barring issues like cracking barrels etc) The odd tire change, hydraulic recoil adjustment, and calibrating/fixing sights. Most of this work is done at RCEME base workshops and not the reserve unit nor the reserve service battalions. If reserve regiments continue to be configured as tools for individual training rather than as a deployable operational resource then there would probably be little need for maintainers at the unit level but there might be a need to upgrade the maintenance capabilities at the support base maintenance unit.
As you may have noticed, I'm a strong advocate of retooling/overhauling the reserve structure to make reserve units (not just arty but all) operationally deployable. That requires a full support structure and, as you point out, the more equipment that there is and the more sophisticated it becomes, the more you will need a full-time maintenance component, either directly within the unit or, alternatively in direct support of the unit, in order to keep the equipment serviceable. Note though that reserve equipment receives much less wear and tear than a comparable Reg F unit's and has more slack time between exercises and equipment usage, so the full-time component could be smaller than a Reg F unit equivalent.
:cheers: