With 9 slots, preferred gemming would be 5 grinder jewels for Speed Sharpening (Good with Razor Sharp), or even 8 upstream jewels for Current Res[Hi] (Good with Olympic Swimmer). It would not be wise to gem away Status Atk Down for the very reason that you will lose Element Atk Up (Unless you use High-Rank kinds which would be a waste of slots). A lot of other jewels can also be used (like Lightfoot/TrapMaster Jewels), it is up to personal preference. To maximize the possible unused slots, combine jewels with Charms.
Another good combination is to have Capture Guru and Speed Sharpening, have a Weapon or Charm with at least one slot or a Charm with at least +2 Perception/Sharpening (more is better) and put 4 Jewels of what Charm you have and 5 of the other, e.g. Charm with +6 Perception, 2 Perception Jewels, 5 Grinder Jewels is what I use and it works well.
If you are Element SnSing, this is the best set to use until after HR51. With 9 slots, it's very flexible, and both Element Attack Up and Razor Sharp is the reason why you should use this. If you are SnSing, the skills to gem in are up to you. Evade+1, Speed Sharpen, Trapmaster, etc. are all good ideas.
This armor is a good armor to bring against Ceadeus because of its Olympic Swimmer to chase it faster, and Razor Sharp, so you don't have to waste too much time on sharpening.
Another good skill to gem into this armor set is Attack Up M. To do this you need to obtain a 2 slotted talisman, 15 Rathalos Scales and 10 Sunspire Jewels. Obviously use the Scales and Jewels to create 5 assault jewels. This way of gemming not only gives you Element Attack Up but also a considerable increase in raw attack.