Training plan advice

Hi all,

I'm currently training for the Dublin marathon at the end of October, which would be my first marathon. My normal training week includes 2 short fast runs and a long slower run. The short runs are 7 miles and I usually run them at my 10K pace (7:05-7:15). My long run has been building steadily for a couple of months now (will do 18 miles this Sunday). 

This week I tried for the first time introducing something a little different. I did hill intervals on Tuesday - 4x0.7m with a quick but easy run downhill in between (+1 mile either side to warm up/down). I plan to do these once a week now, perhaps adding more intervals so increasing from 4 to 6 and then maybe 8. I might alternate this every other week with some flat interval training (800s maybe).

I also plan to introduce another run in the week (so up from 3 runs to 4). This might be a short recovery style run - maybe 4 or 5 miles at a slow pace. And I am also trialling a longer run in place of one of my short runs each week (this week I increased from 7 to 10 miles).

I've been doing a lot of reading about training plans and to be honest it is very difficult to know what approach to take due to the sheer number of different plans, options and opinions. I'm wary of just picking some plan at random as opposed to just going with what I feel is right but at the same time I don't want to base my plan on my own limited knowledge and experience. I did a half marathon in June (trail) and did this in 1:38. I'm aiming for sub 3:30 in the Dublin marathon and confident I can do it as long as my preparation continues in the right direction. 

The question is, is my current training comprehensive enough? Could I be doing better if I varied it a little more. I'm thinking the plan now is: 

Tues: alternating between hill and flat intervals each week. 1m warm up, 4x800-1200metre intevals with jogging in between followed by 1m warm down. 

Wed: 5m at slow pace (8:30 pace?)

Thurs: 10m at steady pace (7:30 pace)

Sun: long run peaking at 20m (8:30-9:00 pace).

If anyone spots any major flaws in my thinking or has any suggested improvements/changes I would greatly appreciate them. 

Cheers,

Dara