The sect is pretty new and I expect that things may change in process of testing, balancing and fine tuning. Advancement recommendations I offer here may be improved as new details discovered.
The Guild is located in the Occultist Guild:
From Cliff face: up;se;e;e;e;d;e;e;e;n;drink blood;e;e;e;chapel;light candle

For advancing see blow, for Spells go HERE.
For Reaver Titles, go here.
For Items, see the Occulist Guild Page.

Rearrange

Reavers combine usage of occult knowledge with considerable fighting training. Primary stats are INT and STR. Having high CON won't hurt, as usual. Dexterity may also be of some use but does not affect special attack or number of Gp.
Wisdom does not seem to be of any importance.

Advancement plan

These are precalculated plans. Final values may slightly differ.
In occult, aim is to have chanting 300 or just a little more, and 2 spell subskills at max. Cursing and enchanting looks like most appropriate to be chosen as primary.
In Fighting, aiming to have max sharp and special at no less than 320 (needed to have invincible slash with 25 str). One less strength requires 18 more special to have slash invincible. Note that plan offered is for max offensive capabilities. It is just one of possible ways.

fighting to 5
fighting.combat to 10
fighting.combat.special to 40
fighting.combat.melee to 15
fighting.combat.melee.sharp to 225

drop 15 levels in fighting.

get sharp to 225 again, leave special at 25 or advance to 27..29 (I'm not so sure about correct rounding)
fighting.combat.melee to 225
fighting.combat to 225
fighting to 225
fighting.points to 225
finish subskills.

sharp should get to about 670(669) and special to 320(321..323) this way.

occult to 5
occult.spells to 10
occult.methods to 10 (only to have 2-hit disruption)
occult.spells.cursing to 250
occult.spells.enchanting to 250

if you wish to do dying/raising, that's the time (have chanting at 20 before losing levels to keep disruption at 2 hits - it will only decrease final values by 1 point).

occult.spells to 250
occult to 250
occult.methods.chanting to 250
occult.methods to 250
finish subskills.

without losing levels, you will end up with 555 in both primary spell skills and 302 in chanting.
losing ten levels will allow to improve primary spell skills to 567..568 and chanting at the end will be about 304-305.

Advancement tips

Following plan above

1 Newbie
I'd advance only fighting to 2-3 just to quickly collect xp to the cap in newbie area. Right after joining, you forget all your skills, but keep all 'points to spend'. Cost all command will give picture like this:

checkpoint:
======SKILLS=======Cur/Max==For Next===========================================
fighting..........   0/225 10450 xp   mental............   0/ 0 mastered
magic.............   0/ 5   8625 xp   occult............   0/250   9900 xp
faith.............   0/ 5   9775 xp   general...........   0/ 20 10350 xp
covert............   0/ 15   2250 xp
======================> You have 1200000 points to spend <=====================

2 Right after joining
ad o to 5
ad o.s to 10
ad o.s.c to 100 (learn disruption spell)
ad o.m to 10 (to get 2-hit disruption)

ad f to 5
ad f.c to 10
ad f.c.s to about 60-80 (to get more gp)
ad f.c.m to 15
ad f.c.m.s to reasonable level or straight to max

3. Depending on situation, in whatever order that would look appropriate...
You may wish to get to level 50 faster to use 'slash' special attack. However, slash will worth using only if you have best weapons. With little skill and low level weapons, it will be less effective than double-hit 'disruption' spell.
If there's no reavers around to spell you up, it would really help to work on enchanting to have your own defensive spells and learn 'gift of steel' faster. Even if they are, it would be better to have it. Effect of 'gift' weakens as you fight and you will be able to dispel and cast it again to keep top shape.
Otherwise, it may be better to work on fighting first.

ad f.c.m.s to improve melee
ad o.s.c to make disruption hit stronger
ad o.s.e to get defensive spells and 'gift of steel'

4. Go on according to advancement plan.
As you may know, losing levels in fighting and occult may improve final picture. Soulskinner can drain fighting, but to lose levels in occult, death is the only way. Decide, do you really want it.

5. General skills do not affect overall level. Do anything anytime if xp gaining is good enough.
g.smithing.armour at 50-100 alows to fix all low level armours

Things to keep in mind:

Overall level is affected by both Fighting and Occult.
Guild points are calculated by both fighting.special and occult.points.

On fighting:

Special attack, 'slash', works since 50 level.
With str 25, slash caps at 320 in special, for str 24 ar 338, for 23 at 356. I did not go further.

On occult:

Animate dead has it maximum bonus when learned.

Quoting interesting parts of spell desctiptions:
Summon Player Ghost: A skill of 300 in occult.methods.chanting will allow the summoning of the corpse as well, if it is in the area.
Disruption: The max number of hits you can choose to inflict is based on your skill in occult.methods.chanting.
(actually, up to 8 hits and it takes less than 300 in chanting to max)

Aura of Steel: The strength of the casting is based both on your enchanting skill and on the corruption in your heart.

Summon Steel: The strength of this weapon is based mostly off of your occult.spells.summoning skill; however, the amount of the enchantment is based upon occult.spells.enchanting.

Veil of Steel: The spell will also protect the target from a percentage of damage which is dependant upon the caster's skill in occult.spells.enchanting.

Bind Wounds (Skill Used : occult.spells.healing) : The power (and likewise the cost) of spell grows with your skill.

Things that are not mentioned at help:
Veil of Steel: maximum percentage of protection of every shielding spell in RoD is limited to 65%. Skill required to get it - is to be found out.
Disruption: damage from each hit grows along with skill in cursing.

Conclusion:
There are only two damaging spells, both in cursing, and I expect that power of both depends on skill in cursing.
Most of spells belong to enchanting and their strength depends on this skill.
There is only one summoning spell (summon steel) that depends on skill, no spells in charming and healing does not require overmaxing.
So, main skills are: methods: chanting, spells: cursing and enchanting. Chosing summoning is under big question.
To the values: chanting at 300 is a must, but looks like no more is necessary.